Vehicle power supply system

ABSTRACT

A vehicle power supply system includes a first power line to which a first inverter and a first battery are connected, a second power line to which a second inverter and a second battery are connected, a voltage converter, a charging and discharging control device that operates the inverters and the voltage converter, and a second regenerable electric power acquisition unit that acquires second regenerable electric power. The charging and discharging control device charges the second battery with second regenerative electric power that is power supplied from the second inverter to the second power line during regenerative deceleration, and supplies second surplus regenerative electric power to the first power line in a case where the second regenerative electric power is larger than the second regenerable electric power, wherein the second surplus regenerative electric power is obtained by excluding the second regenerable electric power from the second regenerative electric power.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Japan Application No.2018-069976, filed on Mar. 30, 2018. The entirety of the above-mentionedpatent application is hereby incorporated by reference herein and made apart of this specification.

BACKGROUND Technical Field

The disclosure relates to a vehicle power supply system. Morespecifically, the disclosure relates to a vehicle power supply systemincluding at least two power storage devices and a motor generator.

Description of Related Art

In recent years, the development of electromotive transport instrumentsincluding an electric motor as a motive power generation source orelectromotive vehicles such as a hybrid vehicle including an electricmotor and an internal-combustion engine as a motive power generationsource has been actively performed. In such electromotive vehicles, anelectric condenser such as a battery or a capacitor is also mounted inorder to supply electrical energy to an electric motor. In addition, inrecent years, a plurality of electric condensers having differentcharacteristics which are mounted in an electromotive vehicle have alsobeen developed.

Patent Document 1 (Japanese Patent Laid-Open No. 2014-143842) disclosesa vehicle power supply system including a low-voltage battery, ahigh-voltage battery, and a converter that converts a voltage. In thevehicle power supply system disclosed in Patent Document 1, thelow-voltage battery is connected to a drive motor through the converter,and the high-voltage battery is connected to the drive motor so as to bein parallel with the converter.

Incidentally, in recent years, an electromotive vehicle in which eachdrive motor is connected to a front wheel and a rear wheel, the frontwheel drive motor and the rear wheel drive motor are driven with powerdischarged from the two kinds of batteries, and all-wheel drivetraveling is possible has also been developed.

In such an electromotive vehicle in which all-wheel drive traveling ispossible, since regenerative electric power is generated in both thefront wheel drive motor and the rear wheel drive motor duringregenerative deceleration, each battery can be charged with regenerativeelectric power supplied from each drive motor. However, in the past,specific ways to supply the regenerative electric power generated inthese two drive motors to the two kinds of batteries so that powerefficiency in the entire vehicle can be improved have not been examinedsufficiently.

SUMMARY

According to an aspect of the disclosure, there is provided a vehiclepower supply system including: a first motor generator connected to afirst wheel of a vehicle; a second motor generator connected to a secondwheel; a first circuit to which a first power converter that transferspower to and from the first motor generator and a first power storagedevice are connected; a second circuit to which a second power converterthat transfers power to and from the second motor generator and a secondpower storage device are connected; a voltage converter that converts avoltage between the first circuit and the second circuit; a charging anddischarging control device that controls charging and discharging of thefirst and second power storage devices by operating the first and secondpower converters and the voltage converter; and a second regenerableelectric power acquisition unit that acquires second regenerableelectric power that is an upper limit for regenerative electric powersupplied to the second power storage device during regenerativedeceleration in which regenerative electric power is generated by thefirst and second motor generators, wherein the charging and dischargingcontrol device charges the second power storage device with secondregenerative electric power that is power supplied from the second powerconverter to the second circuit during the regenerative deceleration,and supplies second surplus regenerative electric power to the firstcircuit through the voltage converter in a case where the secondregenerative electric power is larger than the second regenerableelectric power, wherein the second surplus regenerative electric poweris obtained by excluding the second regenerable electric power from thesecond regenerative electric power.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration of an electromotivevehicle in which a power supply system according to an embodiment of thedisclosure is mounted.

FIG. 2 is a diagram illustrating ranges of use of a first battery and asecond battery.

FIG. 3 is a diagram illustrating portions relating to the execution ofenergy management control among a plurality of control modulesconfigured in an ECU.

FIG. 4A is a diagram schematically illustrating a flow of power realizedin the power supply system when a driving state is a normal travelingstate.

FIG. 4B is a diagram schematically illustrating a flow of power realizedin the power supply system when the driving state is a normal travelingstate.

FIG. 4C is a diagram schematically illustrating a flow of power realizedin the power supply system when the driving state is a normal travelingstate.

FIG. 5 is a diagram schematically illustrating a flow of power realizedin the power supply system when the driving state is a high-outputtraveling state.

FIG. 6A is a diagram schematically illustrating a flow of power realizedin the power supply system when the driving state is a low-outputtraveling state.

FIG. 6B is a diagram schematically illustrating a flow of power realizedin the power supply system when the driving state is a low-outputtraveling state.

FIG. 7A is a diagram schematically illustrating a flow of power realizedin the power supply system when the driving state is a regenerativetraveling state.

FIG. 7B is a diagram schematically illustrating a flow of power realizedin the power supply system when the driving state is a regenerativetraveling state.

FIG. 7C is a diagram schematically illustrating a flow of power realizedin the power supply system when the driving state is a regenerativetraveling state.

FIG. 7D is a diagram schematically illustrating a flow of power realizedin the power supply system when the driving state is a regenerativetraveling state.

FIG. 7E is a diagram schematically illustrating a flow of power realizedin the power supply system when the driving state is a regenerativetraveling state.

FIG. 8A is a diagram schematically illustrating a flow of power realizedin the power supply system when the driving state is an idle state.

FIG. 8B is a diagram schematically illustrating a flow of power realizedin the power supply system when the driving state is an idle state.

FIG. 9A is a diagram schematically illustrating a flow of power realizedin the power supply system when the driving state is a failure travelingstate.

FIG. 9B is a diagram schematically illustrating a flow of power realizedin the power supply system when the driving state is a failure travelingstate.

FIG. 10 is a main flow chart of a driving state determination process ina driving state determination unit.

FIG. 11 is a flow chart illustrating a specific procedure of a normaltraveling determination process.

FIG. 12 is a diagram schematically illustrating a range of a second SOCof the second battery which is realized when the driving state is anormal traveling state.

FIG. 13 is a flow chart illustrating a specific procedure of ahigh-output traveling determination process.

FIG. 14 is a diagram schematically illustrating ranges of a second SOCof the first battery and a second SOC of the second battery which arerealized when the driving state is a high-output traveling state.

FIG. 15 is a flow chart illustrating a specific procedure of alow-output traveling determination process.

FIG. 16 is a diagram schematically illustrating a range of a second SOCof the second battery which is realized when the driving state is alow-output traveling state.

FIG. 17A is a flow chart illustrating of a specific procedure of aregenerative traveling determination process.

FIG. 17B is a flow chart illustrating of a specific procedure of theregenerative traveling determination process.

FIG. 18 is a diagram schematically illustrating a range of a second SOCof the second battery which is realized when the driving state is aregenerative traveling state.

FIG. 19 is a flow chart illustrating a specific procedure of an idledetermination process.

FIG. 20 is a diagram schematically illustrating a range of a second SOCof the second battery which is realized when the driving state is anidle state.

FIG. 21 is a flow chart illustrating a specific procedure of a failuretraveling determination process.

FIG. 22 is a flow chart illustrating a specific procedure of anelectrical pass determination process.

FIG. 23 is a diagram illustrating ranges of a first SOC and a second SOCin which the execution of electrical pass control is permitted in theelectrical pass determination process.

FIG. 24 is a flow chart illustrating a specific procedure of a requiredmotor torque arithmetic process of calculating a first required motortorque and a second required motor torque in a driving forcedistribution calculation unit.

FIG. 25 is a functional block diagram illustrating a procedure ofcalculating required passage power in an energy distribution calculationunit.

FIG. 26 is an example of a map for calculating a target power ratio onthe basis of a second SOC.

DESCRIPTION OF THE EMBODIMENTS

The disclosure provides a vehicle power supply system including at leasttwo power storage devices and a motor generator which makes it possibleto recover regenerative electric power generated in the motor generatorwith high power efficiency.

According to an aspect of the disclosure, there is provided a vehiclepower supply system including: a first motor generator connected to afirst wheel of a vehicle; a second motor generator connected to a secondwheel; a first circuit to which a first power converter that transferspower to and from the first motor generator and a first power storagedevice are connected; a second circuit to which a second power converterthat transfers power to and from the second motor generator and a secondpower storage device are connected; a voltage converter that converts avoltage between the first circuit and the second circuit; a charging anddischarging control device that controls charging and discharging of thefirst and second power storage devices by operating the first and secondpower converters and the voltage converter; and a second regenerableelectric power acquisition unit that acquires second regenerableelectric power that is an upper limit for regenerative electric powersupplied to the second power storage device during regenerativedeceleration in which regenerative electric power is generated by thefirst and second motor generators, wherein the charging and dischargingcontrol device charges the second power storage device with secondregenerative electric power that is power supplied from the second powerconverter to the second circuit during the regenerative deceleration,and supplies second surplus regenerative electric power to the firstcircuit through the voltage converter in a case where the secondregenerative electric power is larger than the second regenerableelectric power, wherein the second surplus regenerative electric poweris obtained by excluding the second regenerable electric power from thesecond regenerative electric power.

According to one or some exemplary embodiments of the disclosure, avehicle accessory that is an electrical load may be connected to thesecond circuit, and the charging and discharging control device maycharge the second power storage device and drive the vehicle accessorywith the second regenerative electric power, and set the second surplusregenerative electric power by excluding the second regenerable electricpower and power required in the vehicle accessory from the secondregenerative electric power.

According to one or some exemplary embodiments of the disclosure, thefirst power storage device may be lower in output weight density andhigher in energy weight density than the second power storage device.

According to one or some exemplary embodiments of the disclosure, thefirst wheel may be a rear wheel and the second wheel is a front wheel,and during the regenerative deceleration, the charging and dischargingcontrol device may operate the first and second power converters so thatthe second regenerative electric power become larger than firstregenerative electric power that is power supplied from the first powerconverter to the first circuit during the regenerative deceleration.

According to one or some exemplary embodiments of the disclosure, thevehicle power supply system may further include: a second power storageparameter acquisition unit that acquires a value of a second powerstorage parameter increasing in accordance with an amount of powerstorage of the second power storage device; and a second regenerationpermission upper limit setting unit that sets a second regenerationpermission upper limit that is a threshold for the second power storageparameter, and in a case where the value of the second power storageparameter is larger than the second regeneration permission upper limitduring the regenerative deceleration, the charging and dischargingcontrol device may prohibit the second power storage device from beingcharged, and may supply at least a portion of the second regenerativeelectric power to the first power storage device through the voltageconverter and the first circuit.

According to one or some exemplary embodiments of the disclosure, thevehicle power supply system may further include: a second power storageparameter acquisition unit that acquires a value of a second powerstorage parameter increasing in accordance with an amount of powerstorage of the second power storage device; and a second regenerationpermission upper limit setting unit that sets a second regenerationpermission upper limit that is a threshold for the second power storageparameter, the charging and discharging control device may prohibit thesecond power storage device from being charged in a case where the valueof the second power storage parameter is larger than the secondregeneration permission upper limit during the regenerativedeceleration, and that the second regeneration permission upper limitsetting unit may change the second regeneration permission upper limiton the basis of a state of the first power storage device.

According to one or some exemplary embodiments of the disclosure, thesecond regeneration permission upper limit setting unit may change thesecond regeneration permission upper limit on the basis of a state ofthe first power storage device.

According to one or some exemplary embodiments of the disclosure, thevehicle power supply system may further include: a first power storageparameter acquisition unit that acquires a value of a first powerstorage parameter increasing in accordance with an amount of powerstorage of the first power storage device; and a first regenerationpermission upper limit setting unit that sets a first regenerationpermission upper limit that is a threshold for the first power storageparameter, in a case where the value of the first power storageparameter is larger than the first regeneration permission upper limit,the second regeneration permission upper limit setting unit may make thesecond regeneration permission upper limit larger than in a case wherethe value of the first power storage parameter is equal to or less thanthe first regeneration permission upper limit, and the charging anddischarging control device may prohibit the first power storage devicefrom being charged in a case where the value of the first power storageparameter is larger than the first regeneration permission upper limitduring the regenerative deceleration.

According to one or some exemplary embodiments of the disclosure, thesecond regeneration permission upper limit setting unit may set thesecond regeneration permission upper limit as a value of any of apredetermined first threshold and a second threshold larger than thefirst threshold, and the second regeneration permission upper limitsetting unit may set the second regeneration permission upper limit asthe first threshold in a case where the value of the second powerstorage parameter is equal to or less than the first threshold duringthe regenerative deceleration, and set the second regenerationpermission upper limit as a value of any of the first threshold and thesecond threshold on the basis of the state of the first power storagedevice in a case where the value of the second power storage parameteris larger than the first threshold and equal to or less than the secondthreshold.

According to one or some exemplary embodiments of the disclosure, thevehicle power supply system may further include a first regenerableelectric power acquisition unit that acquires first regenerable electricpower that is an upper limit for regenerative electric power supplied tothe first power storage device during the regenerative deceleration, andthe second regeneration permission upper limit setting unit may set thesecond regeneration permission upper limit as the second threshold in acase where the value of the second power storage parameter is largerthan the first threshold and equal to or less than the second thresholdduring the regenerative deceleration, and required regenerative electricpower is larger than the first regenerable electric power.

The vehicle power supply system includes the first circuit to which thefirst power converter and the first power storage device are connected,the second circuit to which the second power converter and the secondpower storage device are connected, the voltage converter that convert avoltage between the first circuit and the second circuit, and thecharging and discharging control device that controls charging anddischarging of the first and second power storage devices by operatingthe first and second power converters and the voltage converter. In sucha circuit configuration, in a case where power is transferred betweenthe first circuit and the second circuit through the voltage converter,a loss according to the magnitude of passage power of the voltageconverter occurs. Consequently, the charging and discharging controldevice charges the second power storage device with the secondregenerative electric power supplied from the second power converter tothe second circuit during regenerative deceleration, and supplies thesecond surplus regenerative electric power in which the secondregenerable electric power is excluded from the second regenerativeelectric power to the first circuit through the voltage converter in acase where this second regenerative electric power is larger than thesecond regenerable electric power of the second power storage device.That is, in the vehicle power supply system, the second regenerativeelectric power supplied from the second power converter to the secondcircuit is used in charging of the second power storage device as muchas possible. In a case where an excess portion that is not able to beconsumed occurs in charging of the second power storage device, thisexcess portion is supplied to the first circuit through the voltageconverter. In addition, the second surplus regenerative electric powersupplied to the first circuit can be used in, for example, charging ofthe first power storage device. As described above, according to thevehicle power supply system, since power that passes through the voltageconverter during regenerative deceleration can be reduced as much aspossible, it is possible to recover regenerative electric power suppliedfrom the first and second power converters with high power efficiency.

In the vehicle power supply system, the vehicle accessory is connectedto the second circuit. Thereby, the vehicle accessory can be driven withsecond regenerative electric power supplied from the second powerconverter to the second circuit during regenerative deceleration. Inaddition, in the vehicle power supply system, power in which the secondregenerable electric power and required power in the vehicle accessoryare excluded from the second regenerative electric power is defined asthe second surplus regenerative electric power, and this second surplusregenerative electric power is supplied to the first circuit through thevoltage converter. Therefore, according to the vehicle power supplysystem, since the second surplus regenerative electric power (that is,passage power of the voltage converter) can be further reduced by anamount required in the vehicle accessory, it is possible to furtherimprove power efficiency.

In the vehicle power supply system as described above, the secondregenerative electric power supplied to the second circuit duringregenerative deceleration is supplied to the second power storage deviceas much as possible. Therefore, in the vehicle power supply system, itcan be said that the second power storage device is more likely tomaintain the amount of power storage within a predetermined target rangethan the first power storage device. On the other hand, in the vehiclepower supply system, the first power storage device that is used islower in output weight density and is higher in energy weight densitythan the second power storage device. That is, the first power storagedevice excellent in energy weight density is a capacity-type powerstorage device that is primarily intended for a high capacity, and thesecond power storage device excellent in output weight density is anoutput-type power storage device that is primarily intended for a highoutput. The second power storage device that is such an output type isoften used so as to compensate for a shortage of this first powerstorage device in a case where power requested from a driver is not ableto be covered by the first power storage device alone. For this reason,the amount of power storage of the second power storage device may bemaintained within a predetermined target range in order to meet adriver's request at all times. Therefore, in the vehicle power supplysystem, the second power storage device is formed to have an outputtype, and thus the amount of power storage of the second power storagedevice can be maintained within a target range so as to meet a driver'srequest.

In the vehicle power supply system, the first wheel is defined as a rearwheel, and the second wheel is defined as a front wheel. In addition,the charging and discharging control device operates the first andsecond power converters so that the second regenerative electric powerbecomes larger than the first regenerative electric power duringregenerative deceleration, that is, a larger regenerative braking torqueis imparted to the second wheel that is a front wheel than to the firstwheel that is a rear wheel. Thereby, it is possible to stably brake avehicle. In addition, since it is possible to increase regenerativeelectric power supplied to the second power storage device duringregenerative deceleration by making the second regenerative electricpower larger than the first regenerative electric power in this manner,the amount of power storage of the second power storage device can belikely to be maintained within a target range as described above.

In a case where the value of the second power storage parameter is equalto or less than the second regeneration permission upper limit duringregenerative deceleration, the charging and discharging control devicecharges the second power storage device with the second regenerativeelectric power. In addition, in a case where the value of the secondpower storage parameter is larger than the second regenerationpermission upper limit during regenerative deceleration, the secondpower storage device is prohibited from being charged, and at least aportion of the second regenerative electric power is supplied to thefirst power storage device through the voltage converter and the firstcircuit. According to the vehicle power supply system as describedabove, since power that passes through the voltage converter duringregenerative deceleration can be reduced as much as possible, it ispossible to recover regenerative electric power supplied from the firstand second power converters with high power efficiency.

In the vehicle power supply system, the second regeneration permissionupper limit is set with respect to the second power storage parameter ofthe second power storage device, and the second power storage device isprohibit from being charged in a case where the value of the secondpower storage parameter is larger than the second regenerationpermission upper limit during regenerative deceleration. Thereby, it ispossible to prevent the second power storage device from deterioratingdue to overcharging. Incidentally, in a case where the state of thefirst power storage device is a state in which the supply ofregenerative electric power to this first power storage device isprohibited or limited, an amount that is not able to be recovered by thefirst power storage device in regenerative electric power is required tobe recovered by the second power storage device. Consequently, in thevehicle power supply system, the second regeneration permission upperlimit is set on the basis of the state of the first power storagedevice. Thereby, since charging of the second power storage device canbe prohibited or permitted in accordance with the state of the firstpower storage device, it is possible to recover regenerative electricpower generated in the first and second motor generators with high powerefficiency while preventing the second power storage device from beingovercharged.

According to the vehicle power supply system, the same effect as that ofthe above is exhibited.

In the vehicle power supply system, in a case where the value of thesecond power storage parameter is equal to or less than the firstthreshold during regenerative deceleration, the second regenerationpermission upper limit is set as this first threshold, and in a casewhere the value of the second power storage parameter is larger than thefirst threshold and is equal to or less than the second threshold, thesecond regeneration permission upper limit is set as a value of any ofthe first threshold and the second threshold on the basis of the stateof the first power storage device. Thereby, it is possible to prevent anincrease in a range in which the second power storage device ispermitted to be charged at an unnecessary timing.

In the vehicle power supply system, in a case where the value of thesecond power storage parameter is larger than the first threshold andequal to or less than the second threshold during regenerativedeceleration, and the required regenerative electric power is largerthan the first regenerable electric power (that is, in a case where allthe required regenerative electric power is not able to be recovered bythe first power storage device alone), the second regenerationpermission upper limit is set as the second threshold. Thereby, sincethe second power storage device is permitted to be charged, an excessportion that is not able to be recovered by the first power storagedevice can be recovered by the second power storage device. Thus,according to the vehicle power supply system, it is possible to recoverregenerative electric power generated in the first and second motorgenerators with high power efficiency.

In the vehicle power supply system, the vehicle accessory is connectedto the second circuit, and this vehicle accessory is driven with thesecond regenerative electric power supplied from the second powerconverter to the second circuit during regenerative deceleration. Inaddition, in the vehicle power supply system, in a case where the valueof the second power storage parameter is larger than the first thresholdand equal to or less than the second threshold during regenerativedeceleration, and the required regenerative electric power is largerthan the sum of the first regenerable electric power and power requiredin the vehicle accessory (that is, in a case where all the requiredregenerative electric power is not able to be recovered by the firstpower storage device and the vehicle accessory), the second regenerationpermission upper limit is set as the second threshold. Thereby, sincethe second power storage device is permitted to be charged, an excessportion that is not able to be recovered by the first power storagedevice and the vehicle accessory can be recovered by the second powerstorage device. Thus, according to the vehicle power supply system, itis possible to recover regenerative electric power generated in thefirst and second motor generators with high power efficiency.

Hereinafter, an embodiment of the disclosure will be described withreference to the accompanying drawings.

FIG. 1 is a diagram illustrating a configuration of an electromotivevehicle V (hereinafter, simply referred to as a “vehicle”) in which apower supply system 1 according to the present embodiment is mounted.

The vehicle V includes a first wheel Wr, a second wheel Wf, a firstdrive motor Mr serving as a first motor generator connected to the firstwheel Wr, a second drive motor Mf serving as a second motor generatorconnected to the second wheel Wf, the power supply system 1 thattransfers power to and from these drive motors Mr and Mf, a firstmechanical braking device Br provided in the first wheel Wr, a secondmechanical braking device Bf provided in the second wheel Wf, and anelectronic control unit 7 (hereinafter abbreviated as “ECU”) thatcontrols the power supply system 1, the drive motors Mr and Mf, and themechanical braking devices Br and Bf.

The first wheel Wr is constituted by two wheels, that is, a left wheeland a right wheel. The second wheel Wf is constituted by two wheels,that is, a left wheel and a right wheel. Hereinafter, a case in whichthe first wheel Wr is defined as a rear wheel provided on the rear sideof the vehicle V in its traveling direction, and the second wheel Wf isdefined as a front wheel provided on the front side of the vehicle V inits traveling direction will be described, but the disclosure is notlimited thereto. For example, the first wheel Wr may be defined as afront wheel, and the second wheel Wf may be defined as a rear wheel.

Under the control of the power supply system 1 performed by the ECU 7,the vehicle V can travel in either drive mode of an all-wheel drive mode(hereinafter, also referred to as an “AWD mode”) and a two-wheel drivemode (hereinafter, also referred to as a “2WD mode”). The term “AWDmode” refers to a drive mode in which traveling is performed using boththe first wheel Wr and the second wheel Wf as driving wheels, and theterm “2WD mode” refers to a drive mode in which traveling is performedusing the first wheel Wr as a driving wheel and using the second wheelWf as a driven wheel. As will be described below, the vehicle Vbasically travels in an AWD mode, and travels in a 2WD mode whenpredetermined conditions are established.

A power saving driving request button BM1 and a sports traveling requestbutton BM2 which can be operated by a driver are connected to the ECU 7.In a case where the power saving driving request button BM1 is pressedby a driver, the ECU 7 suppresses the consumption of power in the powersupply system 1 by causing the vehicle V to travel with the drive modepreferentially set to a 2WD mode. In addition, in a case where thesports traveling request button BM2 is pressed by a driver, the ECU 7causes the vehicle V to travel with the drive mode preferentially set toan AWD mode. Meanwhile, as will be described later in detail, in a casewhere a driving state is a high-output traveling state, power stored ina second battery B2 to be described later is frequently used.Consequently, in a case where the sports traveling request button BM2 ispressed, the ECU 7 causes the vehicle V to travel in a recovery mode forquickly recovering the amount of power storage of the second battery B2so as to continuously respond to a high-output traveling request by adriver.

The first drive motor Mr and the second drive motor Mf mainly generatemotive power for causing the vehicle V to travel. The output shafts ofthe respective drive motors Mr and Mf are connected to the wheels Wr andWf through a motive power transfer mechanism which is not shown. Torquesgenerated in the drive motors Mr and Mf by supplying three-phasealternating-current power from the power supply system 1 to the drivemotors Mr and Mf are transferred to the wheels Wr and Wf through themotive power transfer mechanism which is not shown, to rotate the wheelsWr and Wf and cause the vehicle V to travel. In addition, the drivemotors Mr and Mf generate regenerative electric power by acting asgenerators during deceleration of the vehicle V, and impart aregenerative braking torque according to the magnitude of thisregenerative electric power to the wheels Wr and Wf. The regenerativeelectric power generated by the drive motors Mr and Mf is used to chargea first battery B1 and the second battery B2 to be described later whichare included in the power supply system 1.

The first mechanical braking device Br and the second mechanical brakingdevice Bf are constituted by a disc braking system that impartsmechanical braking torques based on friction to the first wheel Wr andthe second wheel Wf. The ECU 7 sets targets for braking torques whichare imparted from the mechanical braking devices Br and Bf to the wheelsWr and Wf by performing a cooperative control process of causingregenerative braking torques imparted from the drive motors Mr and Mf tothe wheels Wr and Wf and mechanical braking torques imparted from themechanical braking devices Br and Bf to the wheels Wr and Wf tocooperate with each other. The mechanical braking devices Bf and Brimpart the mechanical braking torques according to the targetsdetermined by this cooperative control process to the wheels Wr and Wf,and decelerate the vehicle V.

The power supply system 1 includes the first battery B1 serving as afirst power storage device, the second battery B2 serving as a secondpower storage device, a vehicle accessory H serving as an electricalload that consumes power, and a power circuit 2 that connects thesebatteries B1 and B2 and the drive motors Mr and Mf.

The first battery B1 is a secondary battery in which both discharging inwhich chemical energy is converted into electrical energy and chargingin which electrical energy is converted into chemical energy arepossible. Hereinafter, a case in which a so-called lithium-ion storagebattery that performs charging and discharging by lithium ions movingbetween electrodes is used as this first battery B1 will be described,but the disclosure is not limited thereto.

The first battery B1 is provided with a first battery sensor unit 81 inorder to estimate the internal state of the first battery B1. The firstbattery sensor unit 81 is constituted by a plurality of sensors thatdetect physical quantities required for acquiring the charging rate, atemperature or the like of the first battery B1 in the ECU 7 andtransmit signals according to detection values to the ECU 7. Morespecifically, the first battery sensor unit 81 is constituted by avoltage sensor that detects the terminal voltage of the first batteryB1, a current sensor that detects a current flowing through the firstbattery B1, a temperature sensor that detects the temperature of thefirst battery B1, and the like.

The ECU 7 calculates a first power storage parameter increasing inaccordance with the amount of power storage of the first battery B1,more specifically, a charging rate at which the amount of power storageof the first battery B1 is expressed in a percentage, on the basis of aknown algorithm using detection values transmitted from the firstbattery sensor unit 81. Hereinafter, the charging rate of the firstbattery B1 calculated in the ECU 7 using signals transmitted from thefirst battery sensor unit 81 is referred to as a first state of charge(SOC).

The second battery B2 is a secondary battery in which both dischargingin which chemical energy is converted into electrical energy andcharging in which electrical energy is converted into chemical energyare possible. Hereinafter, a case in which a so-called lithium-ionstorage battery that performs charging and discharging by lithium ionsmoving between electrodes is used as this second battery B2 will bedescribed, but the disclosure is not limited thereto. As the secondbattery B2, for example, a capacitor may be used.

The second battery B2 is provided with a second battery sensor unit 82in order to estimate the internal state of the second battery B2. Thesecond battery sensor unit 82 is constituted by a plurality of sensorsthat detect physical quantities required for acquiring the chargingrate, a temperature or the like of the second battery B2 in the ECU 7and transmit signals according to detection values to the ECU 7. Morespecifically, the second battery sensor unit 82 is constituted by avoltage sensor that detects the terminal voltage of the second batteryB2, a current sensor that detects a current flowing through the secondbattery B2, a temperature sensor that detects the temperature of thesecond battery B2, and the like.

The ECU 7 calculates a second power storage parameter increasing inaccordance with the amount of power storage of the second battery B2,more specifically, a charging rate at which the amount of power storageof the second battery B2 is expressed in a percentage, on the basis of aknown algorithm using detection values transmitted from the secondbattery sensor unit 82. Hereinafter, the charging rate of the secondbattery B2 calculated in the ECU 7 using signals transmitted from thesecond battery sensor unit 82 is referred to as a second SOC.

Here, the characteristics of the first battery B1 and thecharacteristics of the second battery B2 will be compared with eachother.

First, the full charging state voltage of the first battery B1 is higherthan the full charging state voltage of the second battery B2.Therefore, during traveling of the vehicle V, the voltage of a firstpower line 21 to be described later to which the first battery B1 isdirectly connected is higher than the voltage of a second power line 22to which the second battery B2 is directly connected.

The first battery B1 is lower in output weight density and is higher inenergy weight density than the second battery B2. In addition, the firstbattery B1 has a larger capacity than the second battery B2. That is,the first battery B1 has more excellent energy weight density than thesecond battery B2. In addition, the second battery B2 has more excellentoutput weight density than the first battery B1. Meanwhile, the energyweight density is the amount of power per unit weight [Wh/kg], and theoutput weight density is power per unit weight [W/kg]. Therefore, thefirst battery B1 that has excellent energy weight density is acapacity-type power storage device that is primarily intended for a highcapacity, and the second battery B2 that has excellent output weightdensity is an output-type power storage device that is primarilyintended for a high output. Therefore, in the power supply system 1, thefirst battery B1 is used as a main power supply, and the second batteryB2 is used as a sub power supply that makes up for the first battery B1that is the main power supply.

FIG. 2 is a diagram illustrating ranges of use of the first battery B1and the second battery B2. The left side of FIG. 2 represents a range ofuse of the first SOC of the first battery B1, and the right side thereofrepresents a range of use of the second SOC of the second battery B2.

In order to prevent the first battery B1 and the second battery B2 fromdeteriorating due to overcharging, in the first SOC[%] and the secondSOC[%], a first usable upper limit and a second usable upper limit areboth set at positions slightly lower than 100%. That is, in a case wherethe first SOC becomes higher than the first usable upper limit, theremay be a concern of the first battery B1 deteriorating. In addition, ina case where the second SOC becomes higher than the second usable upperlimit, there may be a concern of the second battery B2 deteriorating.For this reason, regenerative electric power is prohibited from beingsupplied to the first battery B1 in a case where the first SOC is higherthan the first usable upper limit, and the regenerative electric poweris prohibited from being supplied to the second battery B2 in a casewhere the second SOC is higher than the second usable upper limit.

In addition, in a case where the amount of power storage of a batterydecreases excessively, its voltage also lowers excessively, and thusnecessary power may not be able to be supplied. For this reason, in thefirst SOC and the second SOC, a first usable lower limit and a secondusable lower limit are both set at positions slightly higher than 0%.That is, in a case where the first SOC is set to be equal to or lessthan the first usable lower limit, there may be a concern of requiredpower not being able to be output from the first battery B1. Inaddition, in a case where the second SOC is set to be equal to or lessthan the second usable lower limit, there may be a concern of requiredpower not being able to be output from the second battery B2. For thisreason, the first battery B1 is prohibited from being discharged in acase where the first SOC is equal to or less than the first usable lowerlimit, and the second battery B2 is prohibited from being discharged ina case where the second SOC is equal to or less than the second usablelower limit.

As described above, the usable range of the first battery B1 is betweenthe first usable upper limit and the first usable lower limit, and theusable range of the second battery B2 is between the second usable upperlimit and the second usable lower limit.

Referring back to FIG. 1, the power circuit 2 includes a first inverter3 r that transfers power to and from the first drive motor Mr, a firstpower line 21 serving as a first circuit that connects the DC input andoutput terminal of this first inverter 3 r and the first battery B1, asecond inverter 3 f that transfers power to and from the second drivemotor Mf, a second power line 22 that connects the DC input and outputterminal of this second inverter 3 f, the second battery B2 and thevehicle accessory H, and a voltage converter 4 that connects the firstpower line 21 and the second power line 22.

The first inverter 3 r and the second inverter 3 f are, for example, PWMinverters based on pulse width modulation including a bridge circuitconfigured to bridge-connect a plurality of switching elements (forexample, IGBTs), and have a function of converting direct-current powerand alternating-current power. The first inverter 3 r is connected tothe first power line 21 on its DC input and output side, and isconnected to each coil of the U-phase, V-phase, and W-phase of the firstdrive motor Mr on its AC input and output side. The second inverter 3 fis connected to the second power line 22 on its DC input and outputside, and is connected to each coil of the U-phase, V-phase, and W-phaseof the second drive motor Mf on its AC input and output side. Theinverters 3 r and 3 f drive on/off of a switching element of each phasein accordance with a gate drive signal generated at a predeterminedtiming from a gate drive circuit (not shown) of the ECU 7, to therebyconvert direct-current power in the power lines 21 and 22 intothree-phase alternating-current power and supply the converted power tothe drive motors Mr and Mf, or to convert three-phasealternating-current power supplied from the drive motors Mr and Mf intodirect-current power and supply the converted power to the power lines21 and 22.

The voltage converter 4 connects the first power line 21 and the secondpower line 22, and converts a voltage between the first power line 21and the second power line 22. The voltage converter 4 is a so-calledbidirectional DCDC converter which is configured to combine a reactor, asmoothing capacitor, a plurality of switching elements (for example,IGBTs), and the like, and converts a direct-current voltage between thefirst power line 21 and the second power line 22. The voltage converter4 drives on/off of the plurality of switching elements in accordancewith a gate drive signal generated at a predetermined timing from a gatedrive circuit (not shown) of the ECU 7, to thereby convert a voltagebetween the first power line 21 and the second power line 22.

In the present embodiment, the full charging state voltage of the firstbattery B1 is higher than the full charging state voltage of the secondbattery B2. Therefore, basically, the voltage of the first power line 21is higher than the voltage of the second power line 22. Consequently, ina case where power in the first power line 21 is supplied to the secondpower line 22, the ECU 7 drives the voltage converter 4, and exhibits astepping-down function. The term “stepping-down function” refers to afunction of stepping down power in the first power line 21 which is ahigh-voltage side, outputting the stepped-down power to the second powerline 22, and causing a current to flow from the first power line 21 sideto the second power line 22 side. In addition, in a case where power inthe second power line 22 is supplied to the first power line 21, the ECU7 drives the voltage converter 4, and exhibits a boosting function. Theterm “boosting function” refers to a function of boosting power in thesecond power line 22 which is a low-voltage side, outputting the boostedpower to the first power line 21, and causing a current to flow from thesecond power line 22 side to the first power line 21 side.

The vehicle accessory H is constituted by, for example, a battery heaterthat heats the first battery B1, an air conditioner that regulates thetemperature of a vehicle interior (not shown), a DCDC converter thatcharges an auxiliary battery (not shown), and the like.

The ECU 7 is a microcomputer, and controls charging and discharging ofthe batteries B1 and B2 and a flow of power in the power lines 21 and 22and the voltage converter 4 by operating the inverters 3 r and 3 f, thevoltage converter 4, the mechanical braking devices Br and Bf, and thelike during traveling of the vehicle V. Hereinafter, a detailedprocedure of energy management control performed by the ECU 7 will bedescribed.

FIG. 3 is a diagram illustrating portions relating to the execution ofenergy management control among a plurality of control modulesconfigured in the ECU 7.

The ECU 7 includes a required power calculation unit 70 that calculatesvarious types of required power, a driving state determination unit 71that mainly executes a process relating to the determination of thedriving state of the vehicle V, an inverter control unit 72 that mainlyexecutes a process relating to torque distribution by the drive motorsMr and Mf using a determination result of the driving statedetermination unit 71 or the like and controls the first inverter 3 rand the second inverter 3 f using this process result, a voltageconverter control unit 73 that mainly executes a process relating to ofthe rate of share of charging and discharging of the batteries B1 and B2using the determination result of the driving state determination unit71 or the like and controls the voltage converter 4 using this processresult, a first mechanical braking control unit 74 r and a secondmechanical braking control unit 74 f that control the mechanical brakingdevices Br and Bf using a result of the process relating to torquedistribution in the inverter control unit 72, and a regenerationdetermination unit 75.

The required power calculation unit 70 calculates required power whichis power that is required in various types of devices mounted in thevehicle V. Examples of the required power calculated in the requiredpower calculation unit 70 include vehicle required power and totalrequired power.

The vehicle required power is power required in devices required fordriving the vehicle V, more specifically, the first drive motor Mr andthe second drive motor Mf. The required power calculation unit 70calculates a required driving force of the vehicle V on the basis of adetection value of an accelerator pedal position sensor that detects theposition of an accelerator pedal (not shown) and a detection value of abrake pedal position sensor that detects the position of a brake pedal(not shown), and calculates the vehicle required power on the basis ofthis required driving force. This vehicle required power is set to bepositive during power operations of the drive motors Mr and Mf, and isset to be negative during regenerative operations of the drive motors Mrand Mf.

The total required power is power required in the first power line 21and the second power line 22 of the power supply system 1. The requiredpower calculation unit 70 calculates accessory required power which isrequired power in the vehicle accessory H, and calculates the totalrequired power by adding this accessory required power to the vehiclerequired power.

The regeneration determination unit 75 updates the value of aregeneration flag. The regeneration flag is a flag that clarifies astate in which regenerative traveling where regenerative braking torquesare imparted from the drive motors Mr and Mf to the wheels Wr and Wf ispossible, and can take on a value of “0” or “1.” A value of “0” for theregeneration flag indicates a state in which regenerative traveling isnot possible, and a value of “1” for the regeneration flag indicates astate in which regenerative traveling is possible. The regenerationdetermination unit 75 updates the value of the regeneration flag on thebasis of the detection value of the accelerator pedal position sensor,the brake pedal position sensor, or the like described above.

The driving state determination unit 71 updates values of various typesof flags indicating the driving state of the vehicle V, the usage statesof the batteries B1 and B2, or the like, in accordance with proceduresto be described later with reference to FIGS. 10 to 23, on the basis ofrequired power calculated in the required power calculation unit 70, aregeneration flag updated in the regeneration determination unit 75, andvarious inputs such as the first SOC and the second SOC calculated onthe basis of the detection signals of the battery sensor units 81 and82.

Examples of flags of which the values are updated in the driving statedetermination unit 71 include a driving state flag, a first batteryusage flag, a second battery usage flag, a second SOC consumptionrequest flag, an electrical pass execution flag, a voltage converterdeactivation request flag, a first battery failure flag, and a secondbattery failure flag.

The driving state flag is a flag that clarifies the current drivingstate of the vehicle V, and can take on a value of any of “0,” “1,” “2,”“3,” “4,” and “5.” In the power supply system 1, six driving states,that is, a “normal traveling state,” a “high-output traveling state,” a“low-output traveling state,” a “regenerative traveling state,” an “idlestate,” and a “failure traveling state” are defined as the drivingstates of the vehicle V. A value of “0” for the driving state flagindicates that the driving state is the normal traveling state. A valueof “1” for the driving state flag indicates that the driving state isthe high-output traveling state. A value of “2” for the driving stateflag indicates that the driving state is the low-output traveling state.A value of “3” for the driving state flag indicates that the drivingstate is the regenerative traveling state. A value of “4” for thedriving state flag indicates that the driving state is the idle state. Avalue of “5” for the driving state flag indicates that the driving stateis the failure traveling state.

The first battery usage flag is a flag that clarifies the usage state ofthe first battery B1, and can take on a value of any of “0,” “1,” and“2.” A value of “0” for the first battery usage flag indicates thatcharging and discharge of the first battery B1, that is, both the supplyof power to the first battery B1 and the supply of power from the firstbattery B1 to a load, are permitted. A value of “1” for the firstbattery usage flag indicates a state in which the first battery B1 isprohibited from being discharged. A value of “2” for the first batteryusage flag indicates that the first battery B1 is prohibited from beingcharged.

The second battery usage flag is a flag that clarifies the usage stateof the second battery B2, and can take on a value of any of “0,” “1,”and “2.” A value of “0” for the second battery usage flag indicates thatcharging and discharge of the second battery B2, that is, both thesupply of power to the second battery B2 and the supply of power fromthe second battery B2 to a load, are permitted. A value of “1” for thesecond battery usage flag indicates a state in which the second batteryB2 is prohibited from being discharged. A value of “2” for the secondbattery usage flag indicates that the second battery B2 is prohibitedfrom being charged.

The second SOC consumption flag is a flag that clarifies a state inwhich the second SOC of the second battery B2 is close to the secondusable upper limit, that is, a state in which the consumption of thesecond SOC is required, and can take on a value of any of “0” and “1.” Avalue of “0” for the second SOC consumption flag indicates a state inwhich the consumption of the second SOC is not required. In addition, avalue of “1” for the second SOC consumption flag indicates a state inwhich the consumption of the second SOC is required.

The electrical pass execution flag is a flag that clarifies a state inwhich power discharged from the first battery B1 is supplied to thesecond battery B2 and electrical pass control for charging the secondbattery B2 is executed, and can take on a value of any of “0,” “1,” and“2.” A value of “0” for the electrical pass execution flag indicates astate in which electrical pass control is not executed. A value of “1”for the electrical pass execution flag indicates a state in whichelectrical pass control is executed. In addition, a value of “2” for theelectrical pass execution flag indicates a state in which the executionof electrical pass control is interrupted (that is, a state in which theexecution of electrical pass control is temporarily prohibited).

The voltage converter deactivation request flag is a flag that clarifiesa state in which the deactivation of the voltage converter 4 is requiredin order to reduce a loss occurring in the voltage converter 4, and cantake on a value of any of “0” and “1.” A value of “0” for the voltageconverter deactivation request flag indicates a state in which thedeactivation of the voltage converter 4 is not required, and a value of“1” for the voltage converter deactivation request flag indicates astate in which the deactivation of the voltage converter 4 is required.

The first battery failure flag is a flag that clarifies a state in whichthe first battery B1 is out of order, and can take on a value of any of“0” and “1.” A value of “0” for the first battery failure flag indicatesthat the first battery B1 is normal and is in a usable state. Inaddition, a value of “1” for the first battery failure flag indicatesthat the first battery B1 is out of order and is in an unusable state.

The second battery failure flag is a flag that clarifies a state inwhich the second battery B2 is out of order, and can take on a value ofany of “0” and “1.” A value of “0” for the second battery failure flagindicates that the second battery B2 is normal and is in a usable state.In addition, a value of “1” for the second battery failure flagindicates that the second battery B2 is out of order and is in anunusable state.

Next, a flow of power realized in each driving state will be describedwith reference to FIGS. 4A to 9B.

FIGS. 4A to 4C are diagrams schematically illustrating flows of powerrealized in the power supply system 1 when the driving state is thenormal traveling state. More specifically, FIG. 4A shows a flow of powerrealized in a case where the value of the driving state flag is “0” andthe value of the second battery usage flag is “1,” and FIG. 4B shows aflow of power realized in a case where the value of the driving stateflag is “0” and the value of the electrical pass execution flag is “1.”FIG. 4C shows a flow of power realized in a case where the value of thedriving state flag is “0,” the value of the second battery usage flag is“0,” and the value of the second SOC consumption flag is “1.”

As shown in FIGS. 4A to 4C, in a case where the driving state is thenormal traveling state, the power supply system 1 supplies power to boththe first drive motor Mr and the second drive motor Mf, and performstraveling using the first wheel Wr and the second wheel Wf as drivingwheels. That is, in a case where the driving state is the normaltraveling state, the drive mode of the vehicle V is an AWD mode.

As shown in FIG. 4A, in a case where the driving state is the normaltraveling state, basically, discharging from the second battery B2 tothe second power line 22 is prohibited. Therefore, all power required inthe first drive motor Mr, the second drive motor Mf, and the vehicleaccessory H is covered by power discharged from the first battery B1.That is, a portion of power that is discharged from the first battery B1to the first power line 21 is supplied to the second power line 22through the voltage converter 4, and is consumed in the second drivemotor Mf and the vehicle accessory H.

As shown in FIG. 4B, in a case where electrical pass control is executedwhile the driving state is the normal traveling state, a portion of thepower that is discharged from the first battery B1 is supplied to thesecond battery B2. In this case, all power required in the first drivemotor Mr, the second drive motor Mf, the vehicle accessory H, and thesecond battery B2 is covered by the power that is discharged from thefirst battery B1.

As shown in FIG. 4C, in a case where the value of the second SOCconsumption flag is set to “1” while the driving state is the normaltraveling state, power is discharged from the second battery B2 to thesecond power line 22, and is consumed in the second drive motor Mf andthe vehicle accessory H. Thereby, the consumption of the second SOC ofthe second battery B2 is promoted. Meanwhile, in a case where power isdischarged from the second battery B2 to the second power line 22, theburden of the first battery B1 can be reduced to that extent, and thusit is possible to decrease power flowing from the first power line 21 tothe second power line 22 through the voltage converter 4 more than inthe example of FIG. 4A. Therefore, in a case where the case of FIG. 4Cand the case of FIG. 4A are compared with each other, loss in thevoltage converter 4 is less in the case of FIG. 4C.

FIG. 5 is a diagram schematically illustrating a flow of power realizedin the power supply system 1 when the driving state is the high-outputtraveling state. More specifically, FIG. 5 shows a flow of powerrealized in a case where the value of the driving state flag is “1” andthe value of the second battery usage flag is “0.”

As shown in FIG. 5, in a case where the driving state is the high-outputtraveling state, the power supply system 1 supplies power to both thefirst drive motor Mr and the second drive motor Mf, and performstraveling using the first wheel Wr and the second wheel Wf as drivingwheels. That is, in a case where the driving state is the high-outputtraveling state, the drive mode of the vehicle V is an AWD mode.

In the high-output traveling state, the total required power which ispower required in the power lines 21 and 22 is larger than in the normaltraveling state described with reference to FIGS. 4A to 4C. Thus, asshown in FIG. 5, in a case where the driving state is the high-outputtraveling state, basically, power is discharged from the second batteryB2 to the second power line 22, and is consumed in the second drivemotor Mf and the vehicle accessory H. Thereby, a shortage of power whichis not covered by the first battery B1 alone in the total required poweris compensated for by the second battery B2.

FIGS. 6A and 6B are diagrams schematically illustrating flows of powerrealized in the power supply system 1 when the driving state is thelow-output traveling state. More specifically, FIG. 6A shows a flow ofpower realized in a case where the value of the driving state flag is“2,” the value of the second battery usage flag is “0,” and the value ofthe voltage converter deactivation request flag is “1,” and FIG. 6Bshows a flow of power realized in a case where the value of the drivingstate flag is “2,” the value of the voltage converter deactivationrequest flag is “0,” and the value of the electrical pass execution flagis “1.”

As shown in FIGS. 6A and 6B, in a case where the driving state is thelow-output traveling state, the power supply system 1 supplies requiredpower to the first drive motor Mr, performs traveling using the firstwheel Wr as a driving wheel, and supplies only power required forperforming zero torque control in which the first wheel Wr is followedby the second wheel Wf with a drive torque set to 0 to the second drivemotor Mf. That is, in a case where the driving state is the low-outputtraveling state, the drive mode of the vehicle V is a 2WD mode.

In the low-output traveling state, the power required in the secondpower line 22 is only power required for maintaining the drive torque ofthe second drive motor Mf at 0 and power required in the vehicleaccessory H, and is less than that in the normal traveling state or thehigh-output traveling state described above. Therefore, in thelow-output traveling state, the power that is required in the secondpower line 22 can be covered by power discharged from the second batteryB2 alone. Consequently, as shown in FIG. 6A, in a case where the drivingstate is the low-output traveling state, basically, discharging from thesecond battery B2 to the second power line 22 is permitted, and thepower required for performing zero torque control on the second drivemotor Mf and the power required in the vehicle accessory H are coveredby the second battery B2 alone.

As shown in FIG. 6B, in a case where the second SOC falls below apredetermined threshold while the driving state is the low-outputtraveling state, discharging from the second battery B2 to the secondpower line 22 is prohibited, and electrical pass control is furtherexecuted as necessary. Thereby, a portion of power that is dischargedfrom the first battery B1 to the first power line 21 is supplied to thesecond power line 22 side through the voltage converter 4. Thereby, thepower required for performing zero torque control on the second drivemotor Mf, the power required in the vehicle accessory H, and the powerrequired for charging the second battery B2 are all covered by the powerthat is discharged from the first battery B1.

FIGS. 7A to 7E are diagrams schematically illustrating flows of powerrealized in the power supply system 1 when the driving state is aregenerative traveling state. More specifically, FIG. 7A shows a flow ofpower realized in a case where the value of the driving state flag is“3” and both the values of the first battery usage flag and the secondbattery usage flag are “0,” FIG. 7B shows a flow of power realized in acase where the value of the driving state flag is “3,” the value of thefirst battery usage flag is “0,” and the value of the second batteryusage flag is “2,” FIG. 7C shows a flow of power realized in a casewhere the value of the driving state flag is “3,” the value of the firstbattery usage flag is “2,” and the value of the second battery usageflag is “0,” FIG. 7D shows a flow of power realized in a case where thevalue of the driving state flag is “3” and both the values of the firstbattery usage flag and the second battery usage flag are “2,” and FIG.7E shows a flow of power realized in a case where the value of thedriving state flag is “3” and the value of the electrical pass executionflag is “1.”

In a case where the driving state is a regenerative traveling state, thedrive mode is set as an AWD mode so that as much regenerative electricpower as possible can be recovered by the batteries B1 and B2 and thatlosses in the mechanical braking devices Br and Bf can be reduced.Therefore, in a case where the driving state is a regenerative travelingstate, as shown in FIGS. 7A to 7C and 7E, regenerative electric power isgenerated in the first drive motor Mr and the second drive motor Mf, andis supplied to the first power line 21 and the second power line 22.

As shown in FIG. 7A, in a case where the driving state is a regenerativetraveling state and both the values of the first battery usage flag andthe second battery usage flag are “0,” regenerative electric power thatis supplied from the first drive motor Mr to the first power line 21 isconsumed in charging of the first battery B1, and regenerative electricpower that is supplied from the second drive motor Mf to the secondpower line 22 is consumed in charging of the second battery B2 anddriving of the vehicle accessory H. Meanwhile, as will be describedlater with reference to FIG. 24, a regenerative braking torque impartedto the second wheel that is a front wheel during regenerativedeceleration is larger than a regenerative braking torque imparted tothe first wheel that is a rear wheel. Therefore, the regenerativeelectric power that is supplied from the second drive motor Mf to thesecond power line 22 is larger than the regenerative electric power thatis supplied from the first drive motor Mr to the first power line 21.Therefore, an excess portion that is not able to be consumed in thesecond battery B2 and the vehicle accessory H in the regenerativeelectric power supplied to the second power line 22 is supplied to thefirst battery B1 through the voltage converter 4.

As shown in FIG. 7B, in a case where the driving state is a regenerativetraveling state, the value of the first battery usage flag is “0,” andthe value of the second battery usage flag is “2,” the second battery B2is prohibited from being charged. In addition, a portion that is notable to be consumed in the vehicle accessory H in regenerative electricpower in the second power line 22 is supplied to the first power line 21through the voltage converter 4, and is consumed in charging of thefirst battery B1. Meanwhile, in a case where the example of FIG. 7B andthe example of FIG. 7A are compared with each other, passage power ofthe voltage converter 4 further increases than that in the example ofFIG. 7A to the extent that the second battery B2 is prohibited frombeing charged in the example of FIG. 7B. For this reason, in the exampleof FIG. 7B, a loss in the voltage converter 4 is larger than that in theexample of FIG. 7A.

As shown in FIG. 7C, in a case where the driving state is a regenerativetraveling state, the value of the first battery usage flag is “2,” andthe value of the second battery usage flag is “0,” the first battery B1is prohibited from being charged. Therefore, the regenerative electricpower that is supplied from the first drive motor Mr to the first powerline 21 is supplied to the second power line 22 through the voltageconverter 4. In addition, the regenerative electric power in the secondpower line 22 is consumed in charging of the second battery B2 anddriving of the vehicle accessory H.

As shown in FIG. 7D, in a case where the driving state is a regenerativetraveling state and both values of the first battery usage flag and thesecond battery usage flag are “2,” the first battery B1 and the secondbattery B2 are prohibited from being charged. In this case, theregenerative electric power that is supplied from the drive motors Mrand Mf to the power lines 21 and 22 is set to be 0. In addition, in acase where the regenerative electric power is set to be 0, theregenerative braking torques that are imparted from the drive motors Mrand Mf to the wheels Wr and Wf are also set to be 0. However, in thiscase, mechanical braking torques that are imparted from the mechanicalbraking devices Br and Bf to the wheels Wr and Wf increase, and therebya deceleration operation as required is realized.

As shown in FIG. 7E, in a case where the driving state is a regenerativetraveling state and the value of the electrical pass execution flag isset to “1,” the regenerative electric power that is supplied from thefirst drive motor Mr to the first power line 21 and the power that isdischarged from the first battery B1 to the first power line 21 aresupplied to the second power line 22 through the voltage converter 4. Inaddition, the regenerative electric power that is supplied from thesecond drive motor Mf to the second power line 22 and the power that issupplied from the voltage converter 4 to the second power line 22 areconsumed in charging of the second battery B2 and driving of the vehicleaccessory H.

FIGS. 8A and 8B are diagrams schematically illustrating flows of powerrealized in the power supply system 1 when the driving state is an idlestate. More specifically, FIG. 8A shows a flow of power realized in acase where the value of the driving state flag is “4” and the value ofthe second battery usage flag is “0,” and FIG. 8B shows a flow of powerrealized in a case where the value of the driving state flag is “4” andthe value of the second battery usage flag is “1.”

As shown in FIGS. 8A and 8B, in a case where the driving state is anidle state, the power supply system 1 stops the supply of power to thedrive motors Mr and Mf, and supplies power to only the vehicle accessoryH.

Consequently, in a case where the driving state is an idle state,basically, discharging from the second battery B2 to the second powerline 22 is permitted, and power required in the vehicle accessory H iscovered by the second battery B2. Thereby, in the idle state, since thevoltage converter 4 is deactivated as shown in FIG. 8A and a flow ofpower between the first power line 21 and the second power line 22 canbe interrupted, a loss in the voltage converter 4 can be reduced to 0.

In addition, in a case where the driving state is an idle state, adecrease in the second SOC of the second battery B2 gives rise to aconcern of necessary power not being able to be discharged from thesecond battery B2 during the next acceleration. Consequently, in a casewhere the driving state is an idle state, discharging from the secondbattery B2 to the second power line 22 is prohibited in accordance withthe second SOC of the second battery B2. As shown in FIG. 8B, in a casewhere the second battery B2 is prohibited from being discharged whilethe driving state is an idle state, power that is discharged from thefirst battery B1 is supplied to the vehicle accessory H. In this case,since the power that is discharged from the first battery B1 passesthrough the voltage converter 4, a loss occurs in the voltage converter4 as compared with the case of FIG. 8A, but the consumption of thesecond SOC of the second battery B2 can be suppressed.

FIGS. 9A and 9B are diagrams schematically illustrating flows of powerrealized in the power supply system 1 when the driving state is afailure traveling state. More specifically, FIG. 9A shows a flow ofpower realized in a case where the value of the driving state flag is“5” and the value of the second battery failure flag is “1,” and FIG. 9Bshows a flow of power realized in a case where the value of the drivingstate flag is “5” and the value of the first battery failure flag is“1.”

As shown in FIG. 9A, in a case where the second battery B2 is out oforder, all power required in the first drive motor Mr, the second drivemotor Mf, and the vehicle accessory H is covered by the first batteryB1.

In addition, as shown in FIG. 9B, in a case where the first battery B1is out of order, all power required in the first drive motor Mr, thesecond drive motor Mf, and the vehicle accessory H is covered by thesecond battery B2. However, as described above, the capacity of thesecond battery B2 is smaller than that of the first battery B1.Consequently, in the power supply system 1, in order to make a cruisingdistance based on only the second battery B2 as long as possible,traveling is performed using the second wheel Wf as a driving wheel andusing the first wheel Wr as a driven wheel in a case where the firstbattery B1 is out of order. That is, zero torque control is performed onthe first drive motor Mr using power that is discharged from the secondbattery B2, and power required for the first drive motor Mr is made aslittle as possible. Thereby, it is possible to increase a cruisingdistance after the failure of the first battery B1.

Referring back to FIG. 3, the inverter control unit 72 includes adriving force distribution calculation unit 721, a first gate drivecircuit 722, and a second gate drive circuit 723, and controls the firstinverter 3 r and the second inverter 3 f by using these components.

The driving force distribution calculation unit 721 calculates a firstrequired motor torque for first drive motor Mr and a second requiredmotor torque for the second drive motor Mf so that the flows of powershown in FIG. 4A to FIG. 9B are realized on the basis of required powercalculated by the required power calculation unit 70, a regenerationflag updated by the regeneration determination unit 75, batterycomposition limit power (described later) calculated in the voltageconverter control unit 73, various types of flags updated by the drivingstate determination unit 71, and the like. Similarly to theabove-described vehicle required power, the first required motor torqueand the second required motor torque are set to be positive during poweroperations of the drive motors Mr and Mf, and are set to be negativeduring regenerative operations of the drive motors Mr and Mf. Meanwhile,a specific arithmetic procedure in this driving force distributioncalculation unit 721 will be described later with reference to FIG. 24.

The first gate drive circuit 722 performs switching control on the firstinverter 3 r in accordance with the first required motor torquecalculated in the driving force distribution calculation unit 721.Thereby, a drive torque (in a case where the first required motor torqueis positive) or a regenerative braking torque (in a case where the firstrequired motor torque is negative) having a magnitude according to thefirst required motor torque is imparted from the first drive motor Mr tothe first wheel Wr.

The second gate drive circuit 723 performs switching control on thesecond inverter 3 f in accordance with the second required motor torquecalculated in the driving force distribution calculation unit 721.Thereby, a drive torque (in a case where the second required motortorque is positive) or regenerative braking torque (in a case where thesecond required motor torque is negative) having a magnitude accordingto the second required motor torque is imparted from the second drivemotor Mf to the second wheel Wf.

The first mechanical braking control unit 74 r calculates a first targetbraking torque equivalent to a target for a braking torque that isimparted to the first wheel Wr during deceleration of the vehicle V,calculates a first target mechanical braking torque by subtracting thefirst required motor torque calculated by the driving force distributioncalculation unit 721 from this first target braking torque, and inputsthe calculated torques to the first mechanical braking device Br. Here,the first target braking torque is calculated on the basis of thevehicle required power calculated in the required power calculation unit70. Thereby, in a case where a regenerative braking torque that isimparted from the first drive motor Mr to the first wheel Wr isinsufficient during deceleration of the vehicle V, a mechanical brakingtorque is imparted from the first mechanical braking device Br to thefirst wheel Wr so as to compensate for this insufficiency.

The second mechanical braking control unit 74 f calculates a secondtarget braking torque equivalent to a target for a braking torque thatis imparted to the second wheel Wf during deceleration of the vehicle V,calculates a second target mechanical braking torque by subtracting thesecond required motor torque calculated by the driving forcedistribution calculation unit 721 from this second target brakingtorque, and inputs the calculated torques to the second mechanicalbraking device Bf. Here, the second target braking torque is calculatedon the basis of the vehicle required power calculated in the requiredpower calculation unit 70. Thereby, in a case where a regenerativebraking torque that is imparted from the second drive motor Mf to thesecond wheel Wf is insufficient during deceleration of the vehicle V, amechanical braking torque is imparted from the second mechanical brakingdevice Bf to the second wheel Wf so as to compensate for thisinsufficiency.

The voltage converter control unit 73 includes a composition limit powercalculation unit 731, an energy distribution calculation unit 732, and agate drive circuit 733, and controls the voltage converter 4 by usingthese components.

The energy distribution calculation unit 732 calculate required passagepower for power that passes through the voltage converter 4 so that theflows of power shown in FIGS. 4A to 9B are realized on the basis ofrequired power calculated in the required power calculation unit 70, aregeneration flag updated in the regeneration determination unit 75,various types of flags updated in the driving state determination unit71, and the like. This required passage power is set to be positive, forexample, with respect to the first power line 21 side to the secondpower line 22 side. Meanwhile, a specific arithmetic procedure in thisenergy distribution calculation unit 732 will be described later withreference to FIG. 25.

The gate drive circuit 733 converts the required passage powercalculated by the energy distribution calculation unit 732 into a targetfor a current flowing through the voltage converter 4 from the firstpower line 21 side to the second power line 22 side, and performsswitching control on the voltage converter 4 so that this target isrealized.

Next, a specific arithmetic procedure in the driving state determinationunit 71 will be described with reference to FIGS. 10 to 23.

FIG. 10 is a main flow chart of a driving state determination process inthe driving state determination unit 71. The driving state determinationprocess of FIG. 10 is repeatedly executed in a predetermined controlperiod in the driving state determination unit 71 until a start button(not shown) for starting up the vehicle V is turned on by a driver andthen this start button is turned off.

In S1, the driving state determination unit 71 determines whether thebatteries B1 and B2 are normal on the basis of signals transmitted fromthe battery sensor units 81 and 82. The driving state determination unit71 proceeds to S2 in a case where the determination result of S1 is YES,proceeds to S13 in a case of the determination result is NO, andexecutes a failure traveling determination process to be described laterwith reference to FIG. 21.

In S2, the driving state determination unit 71 determines whether thevehicle V is stopping on the basis of a signal transmitted from avehicle speed sensor (not shown) that detects a vehicle speed that is aspeed of the vehicle V. The driving state determination unit 71 proceedsto S3 in a case where the determination result of S2 is NO, proceeds toS12 in a case where the determination result is YES, and executes anidle determination process to be described later with reference to FIG.19.

In S3, the driving state determination unit 71 determines whether thevalue of the regeneration flag is “1.” The driving state determinationunit 71 proceeds to S4 in a case where the determination result of S3 isNO, proceeds to S11 in a case where the determination result is YES, andexecutes a regenerative traveling determination process to be describedlater with reference to FIGS. 17A and 17B.

In S4, the driving state determination unit 71 determines whether thepower saving driving request button BM1 is pressed. The driving statedetermination unit 71 proceeds to S5 in a case where the determinationresult of S4 is YES, and proceeds to S6 in a case where thedetermination result is NO. In S5, the driving state determination unit71 determines whether the vehicle V is in a cruise state. Morespecifically, the driving state determination unit 71 determines whetherthe vehicle V is in a cruise state by determining whether the requireddriving force is equal to or less than a predetermined driving forceusing a signal transmitted from an accelerator pedal position sensor, asignal transmitted from a front-rear acceleration sensor (not shown)that detects front-rear acceleration of the vehicle V, required motortorques for the drive motors Mr and Mf, and the like. The driving statedetermination unit 71 proceeds to S6 in a case where the determinationresult of S5 is NO, proceeds to S10 in a case where the determinationresult is YES, and executes a low-output traveling determination processto be described later with reference to FIG. 15.

In S6, the driving state determination unit 71 calculates firstoutputtable power which is an upper limit of power capable of beingoutput from the first battery B1, and proceeds to S7. The driving statedetermination unit 71 calculates the first outputtable power on thebasis of, for example, a signal transmitted from the first batterysensor unit 81.

In S7, the driving state determination unit 71 determines whether thetotal required power is larger than the first outputtable power, thatis, all power required in the first power line 21 and the second powerline 22 can be covered by the first battery B1. The driving statedetermination unit 71 proceeds to S8 in a case where the determinationresult of S7 is NO, and executes a normal traveling determinationprocess to be described later with reference to FIG. 11.

In addition, the driving state determination unit 71 proceeds to S9 in acase where the determination result of S7 is YES, and executes ahigh-output traveling determination process to be described later withreference to FIG. 13.

FIG. 11 is a flow chart illustrating a specific procedure of a normaltraveling determination process.

FIG. 12 is a diagram schematically illustrating a range of the secondSOC of the second battery B2 which is realized when the driving state isa normal traveling state.

First, in S21, the driving state determination unit 71 sets the value ofthe driving state flag to “0” so as to clarify that the current drivingstate of the vehicle V is a normal traveling state, and proceeds to S22.

In S22, the driving state determination unit 71 determines whether thevalue of the second SOC consumption flag is “1.” The driving statedetermination unit 71 proceeds to S23 in a case where the determinationresult of S22 is YES, and proceeds to S25 in a case where thedetermination result is NO. This second SOC consumption flag is set to“1” in S26 to be described later, and then is reset to “0” in accordancewith whether the process of S24 to be described later is executed or achange in the value of the driving state flag from “0” to another value.

In S25, the driving state determination unit 71 determines whether thecurrent second SOC of the second battery B2 is equal to or greater thana second normal upper limit determined in advance. This second normalupper limit is a threshold for the second SOC, and is set to be slightlylower than the second usable upper limit at which the supply ofregenerative electric power to the second battery B2 is entirelyprohibited as shown in FIG. 12. The driving state determination unit 71proceeds to S26 in a case where the determination result of S25 is YES,and proceeds to S27 in a case where the determination result is NO.

In S26, in accordance with the determination of the second SOC to beequal to or greater than the second normal upper limit, in other words,in accordance with the determination of the second SOC to increase tothe vicinity of the second usable upper limit, the driving statedetermination unit 71 sets the value of the second SOC consumption flagto “1” and sets the value of the second battery usage flag to “0” so asto secure room for receiving regenerative electric power in the secondbattery B2, and terminates the normal traveling determination process ofFIG. 11.

In S23, the driving state determination unit 71 determines whether thesecond SOC is equal to or less than a consumption end determination SOCdetermined in advance. This consumption end determination SOC is athreshold for the second SOC, and is set to be slightly lower than thesecond normal upper limit as shown in FIG. 12. In a case where thedetermination result of S23 is NO, the driving state determination unit71 proceeds to S26 so as to continuously promote the consumption of thesecond SOC. In addition, in a case where the determination result of S23is YES, the driving state determination unit 71 determines that room forthe second battery B2 to receive regenerative electric power is secured,proceeds to S24, resets the value of the second SOC consumption flag to“0,” and then proceeds to S27.

In S27, the driving state determination unit 71 determines whether thesecond SOC is lower than a second normal lower limit determined inadvance. This second normal lower limit is a threshold for the secondSOC, and is set between the consumption end determination SOC and thesecond usable lower limit as shown in FIG. 12. The driving statedetermination unit 71 proceeds to S28 in a case where the determinationresult of S27 is YES, and proceeds to S29 in a case where thedetermination result is NO.

In S28, in accordance with the determination of the second SOC to belower than the second normal lower limit, in other words, in accordancewith the determination of the second SOC to decrease to the vicinity ofthe second usable lower limit, the driving state determination unit 71sets the value of the electrical pass request flag to “1” so as topromote the recovery of the second SOC of the second battery B2, andthen terminates the normal traveling determination process of FIG. 11.

This electrical pass request flag is a flag that clarifies a state inwhich the execution of electrical pass control described above isrequired, and can take on a value of any of “0” and “1.” A value of “0”for the electrical pass request flag indicates a state in which theexecution of electrical pass control is not required, and a value of “1”for the electrical pass request flag indicates a state in which theexecution of electrical pass control is required. Therefore, inaccordance with the value of the electrical pass request flag being setto “1” in S28, as will be described later with reference to FIG. 22, anelectrical pass determination process of determining whether or not toexecute the electrical pass control is executed.

In addition, in S29, in accordance with the determination of the secondSOC to be equal to or greater than the second normal lower limit, thedriving state determination unit 71 sets the value of the second batteryusage flag to “1” so as to prohibit the second battery B2 from beingdischarged, and then terminates the normal traveling determinationprocess of FIG. 11.

A flow of power realized in the normal traveling determination processof FIG. 11 as described above will be described with reference to FIGS.4A to 4C.

First, as described with reference to FIG. 10, in a case where the totalrequired power is equal to or less than the first outputtable power thatis power capable of being output from the first battery B1 (see S7 ofFIG. 10), that is, in a case where power that is required in theentirety of the combination of the first power line 21 and the secondpower line 22 can be covered by power that is discharged from the firstbattery B1 without using the second battery B2, the driving statebecomes a normal traveling state.

In the normal traveling determination process of FIG. 11, in a casewhere the second SOC is equal to or greater than the second normal lowerlimit and is lower than the second normal upper limit, the value of thesecond battery usage flag is set to “1” (see S29). In accordance withthe value of the second battery usage flag being set in this manner, theinverter control unit 72 and the voltage converter control unit 73operate the inverters 3 r and 3 f and the voltage converter 4 so as torealize the flow of power as shown in FIG. 4A. That is, the invertercontrol unit 72 and the voltage converter control unit 73 prohibitdischarging from the second battery B2 to the second power line 22, andcover all power required in the drive motors Mr and Mf and the vehicleaccessory H by the first battery B1. In a case where the driving stateis a normal traveling state as described above, the total required poweris equal to or less than the first outputtable power of the firstbattery B1, and thus all required power can be covered by the firstbattery B1 as shown in FIG. 4A.

In addition, in the normal traveling determination process of FIG. 11,in a case where the second SOC is equal to or greater than the secondnormal upper limit, the value of the second battery usage flag is set to“0,” and the value of the second SOC consumption flag is set to “1.” Inaccordance with the values of various types of flags being set in thismanner, the inverter control unit 72 and the voltage converter controlunit 73 operate the inverters 3 r and 3 f and the voltage converter 4 soas to realize the flow of power as shown in FIG. 4C. That is, theinverter control unit 72 and the voltage converter control unit 73discharge power from the second battery B2 to the second power line 22so as to promote the consumption of the second SOC of the second batteryB2. In this case, the inverter control unit 72 and the voltage convertercontrol unit 73 operate the inverters 3 r and 3 f and the voltageconverter 4 so as to calculate second required power that is powerrequired in the second power line 22 by adding up power that is requiredin the second drive motor Mf and power that is required in the vehicleaccessory H, and to discharge a shortage of power from the first batteryB1 through the voltage converter 4 to the second power line 22, whereinthe shortage of power is obtained by excluding power discharged by thesecond battery B2 from this second required power. Therefore, while thevalue of the second SOC consumption flag is set to “1,” discharging ofthe second battery B2 is promoted even in a normal traveling state inwhich the second battery B2 is not necessarily required to be used asdescribed above, and the second SOC is consumed.

In addition, in the normal traveling determination process of FIG. 11,the value of the second SOC consumption flag is reset to “0” inaccordance with this value being set to be equal to or less than theconsumption end determination SOC lower than the second normal upperlimit. As will be described later with reference to FIGS. 17A to 18, ina case where the second SOC is equal to or greater than the secondnormal upper limit, charging of the second battery B2 using regenerativeelectric power is further limited than in a case where the second SOC islower than the second normal upper limit. That is, the second normalupper limit is set as a threshold of charging of the second battery B2using regenerative electric power. Consequently, in the normal travelingdetermination process of FIG. 11, the value of the second SOCconsumption flag is continued to be set to “1” until the second SOC isset to be equal to or less than the consumption end determination SOClower than the second normal upper limit, and the consumption of thesecond SOC is promoted. Thereby, in a case where the driving statetransitions from the normal traveling state to the regenerativetraveling state, regenerative electric power generated in the seconddrive motor Mf can be charged in the second battery B2 without beingsubject to the limitation of the second normal upper limit.

In addition, in the normal traveling determination process of FIG. 11,in a case where the second SOC is lower than the second normal lowerlimit, the value of the electrical pass request flag is set to “1.” In acase where the value of the electrical pass request flag is set to “1,”an electrical pass determination process (see FIG. 22 to be describedlater) is executed, and the value of the electrical pass execution flagis set to “1” in accordance with this determination result. In a casewhere the value of the electrical pass execution flag is set to “1” whenthe driving state is a normal traveling state, the inverter control unit72 and the voltage converter control unit 73 operate the inverters 3 rand 3 f and the voltage converter 4 so as to realize the flow of poweras shown in FIG. 4B. That is, the inverter control unit 72 and thevoltage converter control unit 73 operate the inverters 3 r and 3 f andthe voltage converter 4 so that all power required in the first drivemotor Mr, the second drive motor Mf, the vehicle accessory H, and thesecond battery B2 is covered by power that is discharged from the firstbattery B1. Thereby, the second SOC of the second battery B2 isrecovered.

From the above, in a case where the driving state is a normal drivingstate, the second SOC of the second battery B2 is generally maintainedwithin a target convergence range in which the second normal upper limitis set as an upper limit and the second normal lower limit is set as alower limit as shown in FIG. 12.

FIG. 13 is a flow chart illustrating a specific procedure of ahigh-output traveling determination process.

FIG. 14 is a diagram schematically illustrating ranges of the second SOCof the first battery B1 and the second SOC of the second battery B2which are realized when the driving state is a high-output travelingstate.

First, in S31, the driving state determination unit 71 determineswhether the current second SOC of the second battery B2 is lower thanthe second usable lower limit. The driving state determination unit 71proceeds to S32 in a case where the determination result of S31 is YES,and proceeds to S34 in a case where the determination result is NO.

In S32, the driving state determination unit 71 sets the value of thesecond battery usage flag to “1” so as to prohibit second battery B2from being discharged in accordance with the determination of the secondSOC to be lower than the second usable lower limit, further sets thevalue of the driving state flag to “0” so as to clarify that the currentdriving state of the vehicle V is a normal driving state, and proceedsto S33. The high-output traveling determination process of FIG. 13 isexecuted in a case where the total required power is larger than thefirst outputtable power of the first battery B1 as described withreference to FIG. 10. However, since power is not able to be dischargedfrom the second battery B2 in a case where the second SOC is lower thanthe second usable lower limit, a shortage of power is not able to becompensated for by the second battery B2, wherein the shortage of poweris obtained by excluding the first outputtable power from the totalrequired power. In other words, the driving state is not able totransition to a high-output driving state. Therefore, in S32, thedriving state determination unit 71 sets the value of the driving stateflag to “0” so as to set the driving state to a normal traveling state.

In S33, in accordance with the determination of the second SOC to belower than the second usable lower limit, the driving statedetermination unit 71 sets the value of the electrical pass request flagto “1” so as to promote the recovery of the second SOC of the secondbattery B2, and then terminates the high-output traveling determinationprocess of FIG. 13. Thereby, an electrical pass determination process(see FIG. 22 to be described later) of determining whether or not toexecute the electrical pass control is executed.

In S34, the driving state determination unit 71 determines whether thecurrent first SOC of the first battery B1 is lower than a chargingwarning light turn-on level determined in advance. This charging warninglight turn-on level is a threshold for the first SOC, and is set to beslightly higher than the first usable lower limit as shown in FIG. 14.Meanwhile, in a case where the first SOC becomes lower than thischarging warning light turn-on level, a charging warning light providedat a position that can be visually recognized by a driver through aprocess (not shown) is configured to blink. Thereby, a driver canrecognize that the first SOC of the first battery B1 is a small state,and that the power supply system 1 is in a state in which the firstbattery B1 and the second battery B2 are required to be charged. Thedriving state determination unit 71 proceeds to S35 in a case where thedetermination result of S34 is YES, and proceeds to S36 in a case wherethe determination result is NO.

In S35, the driving state determination unit 71 sets the value of thesecond battery usage flag to “1” so as to prohibit the second battery B2from being discharge in order to make a cruising distance as long aspossible. In addition, the driving state determination unit 71 sets thevalue of the driving state flag to “0” so as to set the driving state toa normal traveling state for the same reason as that in S32, and thenterminates the high-output traveling determination process of FIG. 13.

In S36, the driving state determination unit 71 sets the value of thesecond battery usage flag to “0” and sets the value of the driving stateflag to “1” so as to permit discharging of the second battery B2 inaccordance with the determination of the second SOC to be equal to orgreater than the second use lower limit and the determination of thefirst SOC to be equal to or greater than the charging warning lightturn-on level, and terminates the high-output traveling determinationprocess of FIG. 13.

A flow of power realized in the high-output traveling determinationprocess of FIG. 13 as described above will be described with referenceto FIG. 5.

First, the high-output traveling determination process of FIG. 13 isexecuted in a case where the total required power is larger than thefirst outputtable power that is power capable of being output from thefirst battery B1 (see S7 of FIG. 10), that is, in a case where the totalrequired power is not able to be realized unless both the first batteryB1 and the second battery B2 are used.

In the high-output traveling determination process of FIG. 13, in a casewhere the total required power is larger than the first outputtablepower of the first battery B1 as described above (see S7 of FIG. 10),the second SOC is equal to or greater than the second usable lower limit(see S31 of FIG. 13), and the first SOC is equal to or greater than thecharging warning light turn-on level (see S34 of FIG. 13), the value ofthe second battery usage flag is set to “0” and the value of the drivingstate flag is “1.” In accordance with the values of the driving stateflag and the second battery usage flag being set in this manner, theinverter control unit 72 and the voltage converter control unit 73operate the inverters 3 r and 3 f and the voltage converter 4 so as torealize the flow of power as shown in FIG. 5. That is, in a case wherethe total required power is larger than the first outputtable power ofthe first battery B1, the inverter control unit 72 and the voltageconverter control unit 73 operate the inverters 3 r and 3 f and thevoltage converter 4 so that a shortage of power is discharged from thesecond battery B2 to the second power line 22, wherein the shortage ofpower is obtained by excluding an amount that is output by the firstbattery B1 from the total required power. More specifically, theinverter control unit 72 and the voltage converter control unit 73drives the first drive motor Mr using power that is discharged from thefirst battery B1 to the first power line 21, and drives the second drivemotor Mf and the vehicle accessory H so that power in this first powerline 21 is supplied to the second power line 22 side through the voltageconverter 4. In addition, in this case, the inverter control unit 72 andthe voltage converter control unit 73 operate the inverters 3 r and 3 fand the voltage converter 4 so that a shortage is discharged from thesecond battery B2, wherein the shortage is obtained by excluding anamount supplied from the first power line 21 side through the voltageconverter 4 from power required in the second power line 22 (that is,power required in the second drive motor Mf and the vehicle accessoryH). In other words, in a case where the driving state is a high-outputtraveling state, all power that is required in the first power line 21and a portion of power that is required in the second power line 22 arecovered in the first battery B1, and the remaining of power that isrequired in the second power line 22 is covered in the second batteryB2. Thereby, since power that passes through the voltage converter 4 canbe reduced while required power is supplied from the first battery B1and the second battery B2, it is possible to reduce a loss in thisvoltage converter 4.

In addition, in the high-output traveling determination process of FIG.13, in a case where the first SOC is lower than the charging warninglight turn-on level (see S34 of FIG. 13), the value of the secondbattery usage flag is set to “1” and the value of the driving state flagis set to “0.” That is, the second battery B2 is prohibited from beingdischarged, and the driving state is set as a normal traveling state. Inaccordance with the values of the driving state flag and the secondbattery usage flag being set in this manner, the inverter control unit72 and the voltage converter control unit 73 operate the inverters 3 rand 3 f and the voltage converter 4 so as to realize the flow of poweras shown in FIG. 4A. That is, the inverter control unit 72 and thevoltage converter control unit 73 sets the driving state to a normaltraveling state and prohibits the second battery B2 from beingdischarged so that a cruising distance becomes as long as possible.

As described above, in the high-output traveling determination processof FIG. 13, as shown in FIG. 14, in a case where the total requiredpower is larger than the first outputtable upper limit of the firstbattery B1, the first SOC of the first battery B1 is within a firstpermission range in which the charging warning light turn-on level isset as a lower limit and the first usable upper limit is set as an upperlimit, and the second SOC of the second battery B2 is within a secondpermission range in which the second usable lower limit is set as alower limit and the first usable upper limit is set as an upper limit,the driving state is set as a high-output traveling state.

FIG. 15 is a flow chart illustrating a specific procedure of alow-output traveling determination process.

FIG. 16 is a diagram schematically illustrating a range of the secondSOC of the second battery B2 which is realized when the driving state isa low-output traveling state.

First, in S41, the driving state determination unit 71 sets the value ofthe driving state flag to “2” so as to clarify that the current drivingstate of the vehicle V is a low-output traveling state, and proceeds toS42.

In S42, the driving state determination unit 71 determines whether thesecond SOC of the second battery B2 is lower than the second normallower limit. The driving state determination unit 71 proceeds to S43 ina case where the determination result of S42 is NO, and proceeds to S45in a case where the determination result is YES.

In S43, the driving state determination unit 71 sets the value of thesecond battery usage flag to “0” so as to permit discharging of thesecond battery B2, and proceeds to S44. In S44, the driving statedetermination unit 71 sets the value of the voltage converterdeactivation request flag to “1” so as to reduce a loss in the voltageconverter 4, and terminates the low-output traveling determinationprocess of FIG. 15. Meanwhile, this value of the voltage converterdeactivation request flag is reset from “1” to “0” in a case where aprocess of S45 to be described later is executed or the value of thedriving state flag is changes from “2” to another value.

In S45, the driving state determination unit 71 sets the value of thesecond battery usage flag to “1” so as to prohibit the second battery B2from being discharged in accordance with the determination of the secondSOC to be lower than the second normal lower limit, further sets thevalue of the voltage converter deactivation request flag to “0,” andproceeds to S46. In S46, the driving state determination unit 71 setsthe value of the electrical pass request flag to “1” so as to promotethe recovery of the second SOC, and then terminates the low-outputtraveling process of FIG. 15.

A flow of power realized in the low-output traveling determinationprocess of FIG. 15 as described above will be described with referenceto FIGS. 6A and 6B.

First, as described with reference to FIG. 10, in a case where the powersaving driving request button BM1 is pressed and the vehicle is in acruise state (see S4 and S5 of FIG. 10), the driving state is set as alow-output traveling state. In addition, as described with reference toFIGS. 6A and 6B, in a case where the driving state is a low-outputtraveling state, the drive mode of the vehicle V is set as a 2WD mode.

In the low-output traveling determination process of FIG. 15, in a casewhere the driving state is a low-output traveling state and the secondSOC is equal to or greater than the second normal lower limit, the valueof the second battery usage flag is set to “0” (see S43), and the valueof the voltage converter deactivation request flag is set to “1” (seeS44). In accordance with the values of the second battery usage flag andthe voltage converter deactivation request flag being set in thismanner, the inverter control unit 72 and the voltage converter controlunit 73 operate the inverters 3 r and 3 f and the voltage converter 4 soas to realize the flow of power as shown in FIG. 6A. That is, theinverter control unit 72 and the voltage converter control unit 73 stopsa flow of power between the first power line 21 and the second powerline 22 by deactivating the voltage converter 4, and drives the firstdrive motor Mr using power that is discharged from the first battery B1to the first power line 21. In addition, the inverter control unit 72and the voltage converter control unit 73 drives the vehicle accessory Husing power that is discharged from the second battery B2 to the secondpower line 22, and performs zero torque control for operating the secondinverter 3 f so that a drive torque imparted from the second drive motorMf to the second wheel Wf is set to 0 by using power in this secondpower line 22. In this manner, in a case where the driving state is alow-output traveling state and the second SOC of the second battery B2is equal to or greater than the second normal lower limit, a loss in thevoltage converter 4 can be set to 0 by deactivating the voltageconverter 4, driving the vehicle accessory H using power that isdischarged from the second battery B2, and performing zero torquecontrol on the second drive motor Mf.

In addition, in the low-output traveling determination process of FIG.15, in a case where the driving state is a low-output traveling stateand the second SOC is lower than the second normal lower limit, thevalue of the second battery usage flag is set to “1,” the value of thevoltage converter deactivation request flag is set to “0” (see S45), andthe value of the electrical pass request flag is set to “1” (see S46).In accordance with the values of the second battery usage flag, thevoltage converter deactivation request flag, and the electrical passrequest flag being set in this manner, the inverter control unit 72 andthe voltage converter control unit 73 operate the inverters 3 r and 3 fand the voltage converter 4 so as to realize the flow of power as shownin FIG. 6B. That is, the inverter control unit 72 and the voltageconverter control unit 73 discharge power from the first battery B1 tothe first power line 21, drive the first drive motor Mr using power inthis first power line 21, and supply a portion of the power in thisfirst power line 21 to the second power line 22 through the voltageconverter 4. In addition, the inverter control unit 72 and the voltageconverter control unit 73 drive the vehicle accessory H using power inthis second power line 22, perform zero torque control on the seconddrive motor Mf, and further charge the second battery B2.

From the above, in a case where the driving state is a low-outputtraveling state, as shown in FIG. 16, it is possible to performtraveling in a 2WD drive mode having small power consumption in a casewhere the second SOC is within a range in which the second usable lowerlimit is set as a lower limit and the second usable upper limit is setas an upper limit. In addition, particularly in a case where the secondSOC is within a range in which the second normal lower limit is set as alower limit and the second usable upper limit is set as an upper limit,the voltage converter 4 is deactivated as described above, and thustraveling having particularly high power efficiency is possible.

FIGS. 17A and 17B are flows chart illustrating a specific procedure of aregenerative traveling determination process.

FIG. 18 is a diagram schematically illustrating a range of the secondSOC of the second battery B2 which is realized when the driving state isa regenerative traveling state.

First, in S51, the driving state determination unit 71 sets the value ofthe driving state flag to “3” so as to clarify that the current drivingstate of the vehicle V is a regenerative traveling state, and proceedsto S52.

In S52, the driving state determination unit 71 determines whether thesupply of regenerative electric power to the first battery B1 isprohibited, that is, whether first regenerable electric power that is anupper limit of regenerative electric power capable of being supplied tothe first battery B1 is 0. In a case where a regenerative operation isperformed over a long period of time, for example, during travelingalong a downhill road, there may be a concern of electrodepositionoccurring in a battery. For this reason, as will be described later indetail with respect to the composition limit power calculation unit 731,as the execution time of a regenerative operation becomes longer, thisfirst regenerable electric power is brought closer to 0 so as to limitthe supply of regenerative electric power to the first battery B1.Consequently, the driving state determination unit 71 determines whetherthe supply of regenerative electric power to the first battery B1 isprohibited on the basis of a signal transmitted from the first batterysensor unit 81, the duration time of a regenerative operation, or thelike. The driving state determination unit 71 proceeds to S53 in a casewhere the determination result of S52 is NO, and proceeds to S55 in acase where the determination result is YES.

In S53, the driving state determination unit 71 determines whether thefirst SOC of the first battery B1 is higher than the first usable upperlimit. The driving state determination unit 71 proceeds to S54 in a casewhere the determination result of S53 is NO, and proceeds to S55 in acase where the determination result is YES.

In S54, the driving state determination unit 71 sets the value of thefirst battery usage flag to “0” so as to permit the supply ofregenerative electric power to the first battery B1, and proceeds toS56. In addition, in S55, the driving state determination unit 71 setsthe value of the first battery usage flag to “2” so as to prohibit thesupply of regenerative electric power to the first battery B1, andproceeds to S56. As described above, according to the regenerativetraveling determination process of FIGS. 17A and 17B, in a case wherethe first SOC of the first battery B1 is within a first regenerationpermission range in which 0 is set as a lower limit and the first usableupper limit is set as an upper limit (see FIG. 18), the supply ofregenerative electric power to the first battery B1 is permitted exceptwhen the determination result of S52 is YES. That is, in a case wherethe first SOC is out of the first regeneration permission range, thesupply of regenerative electric power to the first battery B1 isprohibited.

In S56, the driving state determination unit 71 determines whether thesupply of regenerative electric power to the second battery B2 isprohibited. The driving state determination unit 71 determines whetherthe second battery B2 is in a state in which regenerative electric poweris prohibited from being supplied on the basis of, for example, a signaltransmitted from the second battery sensor unit 82, the duration time ofa regenerative operation, or the like in the same procedure as S52. Thedriving state determination unit 71 proceeds to S57 in a case where thedetermination result of S56 is NO, and proceeds to S65 in a case wherethe determination result is YES.

In S57, the driving state determination unit 71 determines whether thesecond SOC of the second battery B2 is higher than the second usableupper limit. The driving state determination unit 71 proceeds to S58 ina case where the determination result of S57 is NO, and proceeds to S65in a case where the determination result is YES.

In S58, the driving state determination unit 71 determines whether thesecond SOC of the second battery B2 is higher than the second normalupper limit. The driving state determination unit 71 proceeds to S64 ina case where the determination result of S58 is NO.

In S64, the driving state determination unit 71 sets the value of thesecond battery usage flag to “0” so as to permit the supply ofregenerative electric power to the second battery B2, and terminates theregenerative traveling determination process of FIGS. 17A and 17B. InS65, the driving state determination unit 71 sets the value of thesecond battery usage flag to “2” so as to prohibit the supply ofregenerative electric power to the second battery B2, and terminates theregenerative traveling determination process of FIGS. 17A and 17B.

As described above, according to the regenerative travelingdetermination process of FIGS. 17A and 17B, in a case where the secondSOC of the second battery B2 is within a second basic regenerationpermission range in which 0 is set as a lower limit and the secondnormal upper limit is set as an upper limit (see FIG. 18), the supply ofregenerative electric power to the second battery B2 is permitted exceptwhen the determination result of S56 is YES. In addition, in a casewhere the second SOC is higher than the second usable upper limit, thesupply of regenerative electric power to the second battery B2 isprohibited.

The driving state determination unit 71 executes a regeneration rangeextending process constituted by processes of S59 to S63 in a case wherethe determination result of S58 is YES, that is, in a case where thesecond SOC is higher than the second normal upper limit and is equal toor less than the second usable upper limit. This regeneration rangeextending process is a process of changing the upper limit of aregeneration permission range in which the supply of regenerativeelectric power to the second battery B2 is permitted in accordance withthe state of the first battery B1.

In S59, the driving state determination unit 71 determines whether thevalue of the first battery usage flag that is one of parameters forcharacterizing the state of the first battery B1 is “0.” In a case wherethe determination result of S59 is NO, that is, in a case where thesupply of regenerative electric power to the first battery B1 isprohibited, the driving state determination unit 71 proceeds to S64 soas to be capable of recovering as much regenerative electric power aspossible, and sets the value of the second battery usage flag to “0.”That is, in a case where the supply of regenerative electric power tothe first battery B1 is prohibited, the driving state determination unit71 permits the supply of regenerative electric power to the secondbattery B2 even in a case where the second SOC is higher than the secondnormal upper limit. That is, this is equivalent to the extension of theregeneration permission range, in which the supply of regenerativeelectric power to the second battery B2 is permitted, from the secondbasic regeneration permission range to a second extended regenerationpermission range in which 0 is set as a lower limit and the secondusable upper limit is set as an upper limit (see FIG. 18).

The driving state determination unit 71 proceeds to S60 in a case wherethe determination result of S59 is YES, that is, in a case where thesupply of regenerative electric power to the first battery B1 ispermitted. In S60, the driving state determination unit 71 calculatesrequired regenerative electric power that is a sum of the upper limitsof regenerative electric power capable of being generated in the firstdrive motor Mr and the second drive motor Mf, and proceeds to S61. InS61, the driving state determination unit 71 calculates the firstregenerable electric power that is an upper limit of regenerativeelectric power supplied to the first battery B1, and proceeds to S62.This first regenerable electric power can be calculated by the drivingstate determination unit 71 using, for example, a signal transmittedfrom the first battery sensor unit 81. In S62, the driving statedetermination unit 71 calculates the accessory required power that ispower required in the vehicle accessory H, and proceeds to S63. In S63,the driving state determination unit 71 determines whether the requiredregenerative electric power is larger than the sum of the firstregenerable electric power and the accessory required power.

In a case where the determination result of S63 is YES, that is, in acase where all the required regenerative electric power is not able tobe recovered by the first battery B1 and the vehicle accessory H alone,the driving state determination unit 71 proceeds to S64 so as to becapable of recovering as much regenerative electric power as possible,and sets the value of the second battery usage flag to “0.” That is, ina case where all the required regenerative electric power is not able tobe recovered by the first battery B1 alone, the driving statedetermination unit 71 permits the supply of regenerative electric powerto the second battery B2 even in a case where the second SOC is higherthan the second normal upper limit. That is, this is equivalent to theextension of the regeneration permission range of the second battery B2from the second basic regeneration permission range to the secondextended regeneration permission range (see FIG. 18).

In addition, in a case where the determination result of S63 is NO, thatis, in a case where all the required regenerative electric power is ableto be recovered by the first battery B1 and the vehicle accessory Halone, the driving state determination unit 71 determines that it is notnecessary to extend the upper limit of a regenerable range of the secondbattery B2, proceeds to S65, and sets the value of the second batteryusage flag to “2.”

As described above, in the regeneration range extending processconstituted by S59 to S63, the driving state determination unit 71switches the upper limit of the regeneration permission range in whichthe supply of regenerative electric power to the second battery B2 ispermitted between the second normal upper limit and the second usableupper limit.

A flow of power realized in the regenerative traveling determinationprocess of FIGS. 17A and 17B as described above will be described withreference to FIGS. 7A to 7D.

First, as described with reference to FIG. 10, in a case where the valueof the regeneration flag is “1,” the driving state is set as aregenerative traveling state. In addition, as described with referenceto FIGS. 7A to 7D, in a case where the driving state is a regenerativetraveling state, the drive mode of the vehicle V is set as an AWD mode.Therefore, in the case of the regenerative traveling state, regenerativeelectric power can be generated in both the first drive motor Mr and thesecond drive motor Mf.

According to the regenerative traveling determination process of FIGS.17A and 17B, four states may occur in accordance with a combination ofthe values of the first battery usage flag and the second battery usageflag. The inverter control unit 72 and the voltage converter controlunit 73 realize the flow of power shown in FIG. 7A in a case where boththe values of the first battery usage flag and the second battery usageflag are “0,” realize the flow of power shown in FIG. 7B in a case wherethe value of the first battery usage flag is “0” and the value of thesecond battery usage flag is “2,” realize the flow of power shown inFIG. 7C in a case where the value of the first battery usage flag is “2”and the value of the second battery usage flag is “0,” and realize theflow of power shown in FIG. 7D in a case where both the values of thefirst battery usage flag and the second battery usage flag are “2.”

First, a case where the first SOC is within the first regenerationpermission range and the second SOC is within the second basicregeneration permission range will be described. In this case, accordingto the regenerative traveling determination process of FIGS. 17A and17B, both the values of the first battery usage flag and the secondbattery usage flag can be set to “0.” In accordance with the values ofthe first battery usage flag and the second battery usage flag being setin this manner, the inverter control unit 72 and the voltage convertercontrol unit 73 operate the inverters 3 r and 3 f and the voltageconverter 4 so as to realize the flow of power as shown in FIG. 7A. Thatis, the inverter control unit 72 and the voltage converter control unit73 operate the inverters 3 r and 3 f and the voltage converter 4 so thatregenerative electric power supplied from the first inverter 3 r and thesecond inverter 3 f to the first power line 21 and the second power line22 is supplied to the first battery B1, the second battery B2, and thevehicle accessory H. Here, the inverter control unit 72 and the voltageconverter control unit 73 preferentially charge the second battery B2rather than the first battery B1 in a case where the second SOC is lowerthan the second normal lower limit, that is, in a case where there isroom for the remaining amount of the second battery B2. Morespecifically, the inverter control unit 72 and the voltage convertercontrol unit 73 charge second battery B2 and drive the vehicle accessoryH using second regenerative electric power that is supplied from thesecond inverter 3 f to the second power line 22. In addition, in a casewhere the second regenerative electric power is larger than the sum ofsecond regenerable electric power that is an upper limit of regenerativeelectric power supplied to the second battery B2 and required power inthe vehicle accessory H, the inverter control unit 72 and the voltageconverter control unit 73 supply second surplus regenerative electricpower to the first power line 21 through the voltage converter 4,wherein the second surplus regenerative electric power is obtained byexcluding this sum from the second regenerative electric power. Inaddition, the inverter control unit 72 and the voltage converter controlunit 73 supply power, in which regenerative electric power supplied fromthe first inverter 3 r to the first power line 21 and power supplied tothe first power line 21 through the voltage converter 4 are combinedwith each other, to the first battery B1, and charge the first batteryB1. Thereby, since the second battery B2 is charged with upper-limitpower, the second SOC of the second battery B2 can be quickly recoveredup to the second normal upper limit. In addition, since power thatpasses through the voltage converter 4 can be reduced by preferentiallycharging the second battery B2 in this manner, it is possible to reducea loss in the voltage converter 4.

Next, a case where the first SOC is within the first regenerationpermission range and the second SOC is between the second normal upperlimit and the second usable upper limit will be described. In this case,since the second SOC is close to the second usable upper limit, it canbe said that regenerative electric power is not required to bepositively supplied to the second battery B2. However, according to theregeneration range extending process (S59 to S63) of the regenerativetraveling determination process of FIGS. 17A and 17B, in a case wherethe required regenerative electric power is not able to be recovered bythe first battery B1 alone, the regeneration permission range of thesecond battery B2 is extended to the second extended regenerationpermission range in order to reduce losses in the mechanical brakingdevices Br and Bf, and both the values of the first battery usage flagand the second battery usage flag can be set to “0.” In accordance withthe values of the first battery usage flag and the second battery usageflag being set in this manner, the inverter control unit 72 and thevoltage converter control unit 73 operate the inverters 3 r and 3 f andthe voltage converter 4 so as to realize the flow of power as shown inFIG. 7A similarly to the above example. However, in this case, since thesecond SOC is close to the second usable upper limit, the first batteryB1 is preferentially charged rather than the second battery B2. Morespecifically, the inverter control unit 72 and the voltage convertercontrol unit 73 supply a portion of the second regenerative electricpower, supplied from the second inverter 3 f to the second power line22, to the first power line 21 through the voltage converter 4, supplypower, in which power supplied from the voltage converter 4 to the firstpower line 21 and power supplied from the first inverter 3 r to thefirst power line 21 are combined with each other, to the first batteryB1, and charge the first battery B1. In this time, the inverter controlunit 72 and the voltage converter control unit 73 adjust passage powerof the voltage converter 4 so that the first battery B1 is charged withits upper-limit power (that is, the first regenerable electric power).In addition, the inverter control unit 72 and the voltage convertercontrol unit 73 charge the second battery B2 with the second surplusregenerative electric power, and drive the vehicle accessory H, whereinthe second surplus regenerative electric power is obtained by excludingpower supplied to the first power line 21 through the voltage converter4 from the second regenerative electric power supplied from the secondinverter 3 f to the second power line 22. Thereby, it is possible torecover as much regenerative electric power as possible in the batteriesB1 and B2 while the second battery B2 is prevented from beingovercharged, and to reduce losses in the mechanical braking devices Brand Bf.

Next, a case where the first SOC is within the first regenerationpermission range and the second SOC is higher than the second usableupper limit will be described. In this case, according to theregenerative traveling determination process of FIGS. 17A and 17B, thevalue of the first battery usage flag can be set to “0,” and the valueof the second battery usage flag can be set to “2.” In accordance withthe values of the first battery usage flag and the second battery usageflag being set in this manner, the inverter control unit 72 and thevoltage converter control unit 73 operate the inverters 3 r and 3 f andthe voltage converter 4 so as to realize the flow of power as shown inFIG. 7B. That is, the inverter control unit 72 and the voltage convertercontrol unit 73 prohibit the second battery B2 from being charged, andsupply the second surplus regenerative electric power to the first powerline 21 through the voltage converter 4, wherein the second surplusregenerative electric power is obtained by excluding an amount that isconsumed in the vehicle accessory H from the second regenerativeelectric power supplied from the second inverter 3 f to the second powerline 22. Thereby, the first battery B1 is supplied with power in whichthe first regenerative electric power supplied from the first inverter 3r to the first power line 21 and the second surplus regenerativeelectric power supplied from the voltage converter 4 to the first powerline 21 is combined with each other, and the first battery B1 ischarged. Thereby, it is possible to prevent the second battery B2 frombeing overcharged.

Meanwhile, according to the regenerative traveling determination processof FIGS. 17A and 17B, the flow of power as shown in FIG. 7B can berealized even in a case where the first SOC is within the firstregeneration permission range and the second SOC is between the secondusable upper limit and the second normal upper limit. That is, in theregeneration range extending process (S59 to S63), in a case where it isdetermined that the required regenerative electric power can berecovered by the first battery B1 alone, in other words, even in a casewhere it is determined that the regeneration permission range of thesecond battery B2 is not required to be extended to the second extendedregeneration permission range in the regeneration range extendingprocess, the value of the first battery usage flag is set to “0,” thevalue of the second battery usage flag is set to “2,” and the supply ofregenerative electric power to the second battery B2 is prohibited.Thereby, it is possible to prevent the second battery B2 from beingovercharged.

Next, a case where the first SOC is out of the first regenerationpermission range and the second SOC is lower than the second normalupper limit will be described. In this case, according to theregenerative traveling determination process of FIGS. 17A and 17B, thevalue of the first battery usage flag can be set to “2,” and the valueof the second battery usage flag can be set to “0.” In accordance withthe values of the first battery usage flag and the second battery usageflag being set in this manner, the inverter control unit 72 and thevoltage converter control unit 73 operate the inverters 3 r and 3 f andthe voltage converter 4 so as to realize the flow of power as shown inFIG. 7C. That is, the inverter control unit 72 and the voltage convertercontrol unit 73 prohibit the supply of regenerative electric power tothe first battery B1, and supply all the first regenerative electricpower, supplied from the first inverter 3 r to the first power line 21,to the second power line 22 through the voltage converter 4. Thereby,the second battery B2 and the vehicle accessory H are supplied withpower in which the second regenerative electric power supplied from thesecond inverter 3 f to the second power line 22 and power supplied fromthe voltage converter 4 to the second power line 22 are combined witheach other, whereby the second battery B2 is charged and the vehicleaccessory H is driven. Thereby, since as much regenerative electricpower as possible can be recovered in the second battery B2 and thevehicle accessory H while the first battery B1 is prevented from beingovercharged, it is possible to reduce losses in the mechanical brakingdevices Br and Bf to that extent.

Meanwhile, according to the regenerative traveling determination processof FIGS. 17A and 17B, the flow of power as shown in FIG. 7C can berealized even in a case where the first SOC is out of the firstregeneration permission range and the second SOC is between the secondusable upper limit and the second normal upper limit. In this case, itcan be said that the second SOC is close to the second usable upperlimit, and that regenerative electric power is not required to bepositively supplied to the second battery B2. However, according to theregeneration range extending process (S59 to S63), since theregeneration permission range of the second battery B2 is extended tothe second extended regeneration permission range in a case where thefirst battery B1 is prohibited from being regenerated, the value of thefirst battery usage flag is set to “2,” the value of the second batteryusage flag is set to “0,” and thus the flow of power as shown in FIG. 7Ccan be realized. Thereby, it is possible to recover as much regenerativeelectric power as possible in the second battery B2 and the vehicleaccessory H while the first battery B1 and the second battery B2 areprevented from being overcharged, and to reduce losses in the mechanicalbraking devices Br and Bf.

Next, a case where the first SOC is out of the first regenerationpermission range and the second SOC is also out of the second extendedregeneration permission range will be described. In this case, accordingto the regenerative traveling determination process of FIGS. 17A and17B, both the values of the first battery usage flag and the secondbattery usage flag are set to “2.” In accordance with the values of thefirst battery usage flag and the second battery usage flag being set inthis manner, the inverter control unit 72 and the voltage convertercontrol unit 73 operate the inverters 3 r and 3 f and the voltageconverter 4 so as to realize the flow of power as shown in FIG. 7D. Thatis, the inverter control unit 72 and the voltage converter control unit73 operate the inverters 3 r and 3 f so that both the first regenerativeelectric power supplied from the first inverter 3 r to the first powerline 21 and the second regenerative electric power supplied from thesecond inverter 3 f to the second power line 22 are set to 0. Thereby,although losses in the mechanical braking devices Br and Bf increase,regenerative electric power is not supplied to the first battery B1 andthe second battery B2, and thus these batteries are reliably preventedfrom being overcharged.

FIG. 19 is a flow chart illustrating a specific procedure of an idledetermination process.

FIG. 20 is a diagram schematically illustrating a range of the secondSOC of the second battery B2 which is realized when the driving state isan idle state.

First, in S71, the driving state determination unit 71 sets the value ofthe driving state flag to “4” so as to clarify that the current drivingstate of the vehicle V is an idle state, and proceeds to S72.

In S72, the driving state determination unit 71 determines whether thesecond SOC of the second battery B2 is lower than the second normallower limit. The driving state determination unit 71 proceeds to S73 ina case where the determination result of S72 is NO, and proceeds to S75in a case where the determination result is YES.

In S73, the driving state determination unit 71 sets the value of thesecond battery usage flag to “0” so as to permit discharging of thesecond battery B2, and proceeds to S74. In S74, the driving statedetermination unit 71 sets the value of the voltage converterdeactivation request flag to “1” so as to reduce a loss in the voltageconverter 4, and terminates the idle determination process of FIG. 19.Meanwhile, this value of the voltage converter deactivation request flagis reset from “1” to “0” in a case where a process of S76 to bedescribed later is executed or the value of the driving state flag ischanged from “4” to another value.

In S75, the driving state determination unit 71 sets the value of thesecond battery usage flag to “1” so as to prohibit the second battery B2from being discharged, and proceeds to S76. In S76, the driving statedetermination unit 71 sets the value of the voltage converterdeactivation request flag to “0” so as to drive the vehicle accessory Hwith power that is supplied from the first battery B1, and terminatesthe idle determination process of FIG. 19.

A flow of power realized in the idle determination process of FIG. 19 asdescribed above will be described with reference to FIGS. 8A and 8B.

According to the idle determination process of FIG. 19, in a case wherethe second SOC of the second battery B2 is equal to or greater than thesecond normal lower limit, the value of the driving state flag is set to“4,” and the value of the second battery usage flag is set to “0.” Inaccordance with the values of these flags being set as described above,the inverter control unit 72 and the voltage converter control unit 73operate the voltage converter 4 so as to realize the flow of power asshown in FIG. 8A. That is, the voltage converter 4 is deactivated, aflow of power between the first power line 21 and the second power line22 is interrupted, and the vehicle accessory H is driven with power thatis discharged from the second battery B2. Thereby, it is possible todrive the vehicle accessory H while a loss in the voltage converter 4 isset to 0.

In addition, according to the idle determination process of FIG. 19, ina case where the second SOC of the second battery B2 is lower than thesecond normal lower limit, the value of the driving state flag is set to“4,” and the value of the second battery usage flag is set to “1.” Inaccordance with the values of these flags being set as described above,the inverter control unit 72 and the voltage converter control unit 73operate the voltage converter 4 so as to realize the flow of power asshown in FIG. 8B. That is, the second battery B2 is prohibited frombeing discharged, power that is supplied from the first battery B1 tothe first power line 21 is supplied to the second power line 22 throughthe voltage converter 4, and the vehicle accessory H is driven withpower in this second power line 22. Thereby, it is possible to drive thevehicle accessory H even in a case where the second SOC of the secondbattery B2 is in a low state.

From the above, in a case where the driving state is an idle state andthe second SOC is within a range in which the second normal lower limitis set as a lower limit and the second usable upper limit is set to anupper limit, it is possible to drive the vehicle accessory H while thevoltage converter 4 is deactivated.

FIG. 21 is a flow chart illustrating a specific procedure of a failuretraveling determination process.

First, in S81, the driving state determination unit 71 sets the value ofthe driving state flag to “5” so as to clarify that the current drivingstate of the vehicle V is a failure traveling state, and proceeds toS82.

In S82, the driving state determination unit 71 determines whether abattery that is out of order is the first battery B1. In a case wherethe determination result of S82 is NO, that is, in a case where thesecond battery B2 is out of order, the driving state determination unit71 proceeds to S83, sets the value of the second battery failure flag to“1,” and terminates the failure traveling determination process of FIG.21.

In addition, in a case where the determination result of S82 is YES,that is, in a case where the first battery B1 is out of order, thedriving state determination unit 71 proceeds to S84, sets the value ofthe first battery failure flag to “1,” and terminates the failuretraveling determination process of FIG. 21.

A flow of power realized in the failure traveling determination processof FIG. 21 as described above will be described with reference to FIGS.9A and 9B.

According to the failure traveling determination process of FIG. 21, ina case where the second battery B2 is out of order, the value of thedriving state flag is set to “5,” and the value of the second batteryfailure flag is set to “1.” In accordance with the values of these flagsbeing set as described above, the inverter control unit 72 and thevoltage converter control unit 73 operate the voltage converter 4 so asto realize the flow of power as shown in FIG. 9A. That is, the invertercontrol unit 72 and the voltage converter control unit 73 operate theinverters 3 r and 3 f and the voltage converter 4 so that all powerrequired in the first drive motor Mr, the second drive motor Mf, and thevehicle accessory H is supplied from the first battery B1. Thereby, itis possible to continue traveling of the vehicle V even in a case wherethe second battery B2 is out of order.

In addition, according to the failure traveling determination process ofFIG. 21, in a case where the first battery B1 is out of order, the valueof the driving state flag is set to “5,” and the value of the firstbattery failure flag is set to “1.” In accordance with the values ofthese flags being set as described above, the inverter control unit 72and the voltage converter control unit 73 operate the voltage converter4 so as to realize the flow of power as shown in FIG. 9B. That is, theinverter control unit 72 and the voltage converter control unit 73 drivethe second drive motor Mf and the vehicle accessory H with power that isdischarged from the second battery B2. In addition, the inverter controlunit 72 and the voltage converter control unit 73 supply a portion ofpower, discharged from the second battery B2 to the second power line22, to the first power line 21 through the voltage converter 4, andperform zero torque control for operating the first inverter 3 r so thata drive torque imparted from the first drive motor Mr to the first wheelWr using power in this first power line 21 is set to 0. Thereby, it ispossible to continue traveling of the vehicle V even in a case where thefirst battery B1 is out of order.

FIG. 22 is a flow chart illustrating a specific procedure of anelectrical pass determination process. This electrical passdetermination process is a process of permitting or prohibiting theexecution of electrical pass control for charging the second battery B2using power discharged from the first battery B1. This electrical passdetermination process is repeatedly executed in a predetermined controlperiod in the driving state determination unit 71 until the value of theelectrical pass request flag is set to “1” and then the value of theelectrical pass request flag is set to “0” in a process of S99 to bedescribed later.

FIG. 23 is a diagram illustrating ranges of the first SOC and the secondSOC in which the execution of electrical pass control is permitted inthe electrical pass determination process.

First, in S91, the driving state determination unit 71 determineswhether a recovery mode is being executed. More specifically, thedriving state determination unit 71 determines whether the recovery modeis being executed depending on, for example, whether the sportstraveling request button BM2 is pressed.

The driving state determination unit 71 proceeds to S92 in a case wherethe determination result of S91 is NO. In S92, the driving statedetermination unit 71 determines whether power discharged from the firstbattery B1 is supplied to the second drive motor Mf through the voltageconverter 4.

The driving state determination unit 71 proceeds to S93 in a case wherethe determination result of S92 is YES. In addition, the driving statedetermination unit 71 proceeds to S99 in a case where the determinationresult of S92 is NO, that is, in a case where power discharged from thefirst battery B1 is not supplied to the second drive motor Mf throughthe voltage converter 4. In S99, the driving state determination unit 71determines not to be an appropriate time to execute electrical passcontrol, resets both the values of the electrical pass execution flagand the electrical pass request flag to “0,” and terminates theelectrical pass determination process of FIG. 22.

Here, in the determination process in S92, a case where the execution ofelectrical pass control is not permitted, that is, a case where powerdischarged from the first battery B1 is not supplied to the second drivemotor Mf through the voltage converter 4 specifically refers to, forexample, a state in which the voltage converter 4 is deactivated.Therefore, in a case where the driving state is a driving state in whichthe voltage converter 4 is deactivated, more specifically, in a casewhere it is a low-output traveling state (see FIG. 6A) in which thedrive mode is set as a 2WD drive mode or an idle state (see FIG. 8A),the execution of electrical pass control is not permitted.

In a case where the determination result of S91 is YES, the drivingstate determination unit 71 proceeds to S93 without going through thedetermination of S92. That is, in a case where the recovery mode forquickly recovering the second SOC is being executed, the driving statedetermination unit 71 permits the execution of electrical pass controleven in a case where a drive torque greater than 0 is not imparted fromthe second drive motor Mf to the second wheel Wf. Thereby, in a casewhere the recovery mode is being executed, there are increasing chancesfor the execution of electrical pass control to be permitted, whereby itis possible to quickly recover the second SOC.

In S93, the driving state determination unit 71 determines whether thevalue of the electrical pass execution flag is “1” or “2.” The drivingstate determination unit 71 proceeds to S94 in a case where thedetermination result of S93 is NO, that is, in a case where theelectrical pass control is not being executed or interrupted. Thedriving state determination unit 71 proceeds to S95 in a case where thedetermination result of S93 is YES.

In S94, the driving state determination unit 71 acquires the first SOCof the first battery B1 and the second SOC of the second battery B2, anddetermines whether the first SOC and the second SOC are withinpredetermined electrical pass permission ranges, respectively. Thedriving state determination unit 71 proceeds to S95 in a case where thedetermination result of S94 is YES, and proceeds to S99 in a case wherethe determination result is NO.

Electrical pass permission ranges for the first and second SOCs will bedescribed with reference to FIG. 23.

First, in a case where electrical pass control is executed, power isdischarged from the first battery B1, and thus the first SOC decreases.In addition, in a case where the electrical pass control is executed,power flows through the voltage converter 4, and thus a loss occurs.Consequently, in a case where the first SOC is lower than the chargingwarning light turn-on level, the driving state determination unit 71prohibits the electrical pass control from being executed so as tosecure a cruising distance of the vehicle V. Therefore, a firstelectrical pass permission range for the first SOC is a range equal toor greater than the charging warning light turn-on level. In addition,since a loss occurs in a case where the electrical pass control isexecuted as described above, the electrical pass control may not befrequently executed in terms of energy efficiency. Consequently, in acase where the second SOC is equal to or greater than the second normallower limit, the driving state determination unit 71 prohibits theelectrical pass control from being executed. Therefore, a secondelectrical pass permission range for the second SOC is a range less thanthe second normal lower limit. In a case where at least any of the firstSOC and the second SOC is out of its electrical pass permission range inS94, the driving state determination unit 71 proceeds to S99, andprohibits the electrical pass control from being executed. In addition,in a case where both the first SOC and the second SOC is within itselectrical pass permission range, the driving state determination unit71 proceeds to S95.

In S95, the driving state determination unit 71 determines whether thedriving state is a high-output traveling state, in other words, whetherthe total required power is larger than the first outputtable power ofthe first battery B1. In a case where the driving state is a high-outputtraveling state as described above, the total required power exceeds thefirst outputtable power of the first battery B1, and thus it isnecessary to discharge power from the second battery B2 in order to meetthis requirement. For this reason, it is not possible to execute theelectrical pass control. Consequently, in a case where the determinationresult of S95 is YES, the driving state determination unit 71 proceedsto S100. In S100, the driving state determination unit 71 sets the valueof the electrical pass execution flag to “2” so as to interrupt (thatis, temporarily prohibit) the execution of the electrical pass control,and terminates the electrical pass determination process of FIG. 22.

In a case where the determination result of S95 is NO, the driving statedetermination unit 71 proceeds to S96. In S96, the driving statedetermination unit 71 determines whether the recovery mode is beingexecuted in the same procedure as S91 described above. In a case wherethe determination result of S96 is NO, the driving state determinationunit 71 proceeds to S97.

In S97, the driving state determination unit 71 determines whether thedriving state is a regenerative traveling state. In a case where thedriving state is a regenerative traveling state as described above, theinverters 3 r and 3 f and the voltage converter 4 are operated so thatas much regenerative electric power as possible is recovered by thefirst and second batteries B1 and B2. Therefore, in a case where theelectrical pass control is intended to be executed when the drivingstate is a regenerative traveling state, regenerative electric power isnot able to be efficiently recovered, and thus there may be a concern oflosses in the mechanical braking devices Br and Bf increasing.Consequently, the driving state determination unit 71 proceeds to S100in a case where the determination result of S97 is YES, sets the valueof the electrical pass execution flag to “2” so as to interrupt (thatis, temporarily prohibit) the execution of the electrical pass control,and terminates the electrical pass determination process of FIG. 22.

In addition, in a case where the determination result of S96 is YES, thedriving state determination unit 71 proceeds to S98 without executingthe process of S97. That is, in a case where the recovery mode is beingexecuted, the driving state determination unit 71 permits the executionof the electrical pass control even when the driving state is aregenerative traveling state so as to meet this requirement. Thereby, ina case where the recovery mode is being executed, there are increasingchances for the execution of electrical pass control to be permitted,whereby it is possible to quickly recover the second SOC.

In S98, the driving state determination unit 71 determines whether atime to terminate the execution of the electrical pass control hasarrived. More specifically, the driving state determination unit 71determines that a time to terminate the execution of the electrical passcontrol has arrived, for example, in a case where the second SOC isequal to or greater than the second normal upper limit. In a case wherethe determination result of S98 is YES, the driving state determinationunit 71 proceeds to S99, resets both the values of the electrical passexecution flag and the electrical pass request flag to “0,” andterminates the electrical pass determination process of FIG. 22.

In addition, in a case where the determination result of S98 is NO, thedriving state determination unit 71 proceeds to S101. In S101, thedriving state determination unit 71 sets the value of the electricalpass execution flag to “1” so as to execute the electrical pass control,and terminates the electrical pass determination process of FIG. 22.

Referring back to FIG. 3, the composition limit power calculation unit731 calculates battery composition limit power of a virtual batteryobtained by combining the first battery B1 with the second battery B2 byusing signals transmitted from the battery sensor units 81 and 82, thevalues of the first and second battery usage flags or the values of thefirst and second battery failure flags updated in the driving statedetermination unit 71, or the like. This battery composition limit poweris constituted by outputtable power and regenerable electric power.

The outputtable power is an upper limit of power capable of being outputfrom a virtual battery obtained by combining the first battery B1 withthe second battery B2, and is positive. In addition, the regenerableelectric power is an upper limit of power capable of being supplied tothe virtual battery obtained by combining the first battery B1 with thesecond battery B2, and is negative.

The composition limit power calculation unit 731 calculates powercapable of being output through the following procedure. First, thecomposition limit power calculation unit 731 uses signals transmittedfrom the first battery sensor unit 81 and the second battery sensor unit82 to calculate the first outputtable power that is power capable ofbeing output by the first battery B1 and the second outputtable powerthat is power capable of being output by the second battery B2 bysearching, for example, a map that is not shown. In addition, thecomposition limit power calculation unit 731 refers to the first batteryusage flag, the first battery failure flag, the second battery usageflag, and the second battery failure flag to specify a battery out ofthe first battery B1 and the second battery B2 which is in a state wheredischarging is prohibited or discharging is not possible.

In addition, in a case where power is required in the vehicle accessoryH, power capable of being output by the first battery B1 and the secondbattery B2 is limited to required power of this vehicle accessory H.Thus, the composition limit power calculation unit 731 acquires therequired power of the vehicle accessory H. The composition limit powercalculation unit 731 sets power, obtained by subtracting the requiredpower of the vehicle accessory H from the sum of the first outputtablepower and the second outputtable power, as outputtable power in a casewhere both the first battery B1 and the second battery B2 are not in astate in which discharging is prohibited or discharging is not possible,sets power, obtained by subtracting the required power of the vehicleaccessory H from the second outputtable power, as outputtable power in acase where only the first battery B1 is in a state in which dischargingis prohibited or discharging is not possible, sets power, obtained bysubtracting the required power of the vehicle accessory H from the firstoutputtable power, as outputtable power in a case where only the secondbattery B2 is in a state in which discharging is prohibited ordischarging is not possible, and sets outputtable power to 0 in a casewhere both the first battery B1 and the second battery B2 are in a statein which discharging is prohibited or discharging is not possible.

In addition, the composition limit power calculation unit 731 calculatesregenerable electric power in the following procedure. First, thecomposition limit power calculation unit 731 uses the signalstransmitted from the first battery sensor unit 81 and the second batterysensor unit 82 to calculate a basic value for the first regenerableelectric power that is power capable of being supplied to the firstbattery B1 and a basic value for the second regenerable electric powerthat is power capable of being supplied to the second battery B2 bysearching, for example, a map that is not shown. In addition, in a casewhere a regenerative operation is performed over a long period of time,for example, during traveling along a downhill road, and regenerativeelectric power is continuously supplied to the batteries B1 and B2,there may be a concern of electrodeposition occurring in these batteriesB1 and B2. Consequently, the composition limit power calculation unit731 calculates a correction value on the basis of the execution time ofthe regenerative operation so that the first and second regenerableelectric powers are brought closer to 0 as the execution time of theregenerative operation becomes longer. In addition, the compositionlimit power calculation unit 731 calculates the first regenerableelectric power and the second regenerable electric power by adding upthe basic value calculated on the basis of the map as described aboveand the correction value calculated on the basis of the execution timeof the regenerative operation. In addition, the composition limit powercalculation unit 731 refers to the first battery usage flag, the firstbattery failure flag, the second battery usage flag, and the secondbattery failure flag to specify a battery out of the first battery B1and the second battery B2 which is in a state where regeneration isprohibited or regeneration is not possible.

In addition, in a case where power is required in the vehicle accessoryH, regenerative electric power can be consumed by the vehicle accessoryH, and thus it is possible to load the required power of this vehicleaccessory H on the regenerable electric power. The composition limitpower calculation unit 731 sets the sum of the first regenerableelectric power, the second regenerable electric power and the requiredpower of the vehicle accessory H as regenerable electric power in a casewhere both the first battery B1 and the second battery B2 are not in astate in which regeneration is prohibited or regeneration is notpossible, sets the sum of the second regenerable electric power and therequired power of the vehicle accessory H as regenerable electric powerin a case where only the first battery B1 is in a state in whichregeneration is prohibited or regeneration is not possible, sets the sumof the first regenerable electric power and the required power of thevehicle accessory H as regenerable electric power in a case where onlythe second battery B2 is in a state in which regeneration is prohibitedor regeneration is not possible, and sets regenerable electric power to0 in which both the first battery B1 and the second battery B2 are in astate in which regeneration is prohibited or regeneration is notpossible.

Next, a specific arithmetic procedure in the driving force distributioncalculation unit 721 will be described with reference to FIG. 24.

FIG. 24 is a flow chart illustrating a specific procedure of a requiredmotor torque arithmetic process of calculating a first required motortorque and a second required motor torque in the driving forcedistribution calculation unit 721. In the driving force distributioncalculation unit 721, the first required motor torque and the secondrequired motor torque are calculated by repeatedly executing the processshown in FIG. 24 for each predetermined control period.

First, in S201, the driving force distribution calculation unit 721refers to the values of the regeneration flag and the driving state flagto calculate a first torque ratio Rr indicating a ratio of the torque ofthe first drive motor Mr to the total torque and a second torque ratioRf indicating a ratio of the torque of the second drive motor Mf to thetotal torque, and proceeds to S202.

In a case where the value of the regeneration flag is “0” and the valueof the driving state flag is not “2” (that is, in the case of not beinga low-output traveling state in which the drive mode is set as a 2WDmode), the driving force distribution calculation unit 721 calculatesthe first torque ratio Rr and the second torque ratio Rf so that a ratiobetween the torque of the first drive motor Mr and the torque of thesecond drive motor Mf is configured such that, for example, the torqueof the first drive motor Mr becomes larger than the torque of the seconddrive motor Mf, more specifically, is set to, for example, 75:25. Thatis, in this case, the first torque ratio Rr is set to 0.75, and thesecond torque ratio Rf is set to 0.25.

In a case where the value of the regeneration flag is “0” and the valueof the driving state flag is “2,” the driving force distributioncalculation unit 721 calculates the first torque ratio Rr and the secondtorque ratio Rf so that the ratio between the torque of the first drivemotor Mr and the torque of the second drive motor Mf is set to 100:0.That is, in this case, the first torque ratio Rr is set to 1.00, and thesecond torque ratio Rf is set to 0.00. Thereby, in a low-outputtraveling state in which the drive mode is set as a 2WD mode, the secondrequired motor torque is set to 0, and the zero torque control of thesecond drive motor Mf is executed (see FIGS. 6A and 6B).

In addition, in a case where the value of the regeneration flag is “0,”the value of the driving state flag is “5,” and the value of the firstbattery failure flag is “1,” the driving force distribution calculationunit 721 calculates the first torque ratio Rr and the second torqueratio Rf so that the ratio between the torque of the first drive motorMr and the torque of the second drive motor Mf is set to 0:100. That is,in this case, the first torque ratio Rr is set to 0.00, and the secondtorque ratio Rf is set to 1.00. Thereby, in a case where the firstbattery B1 is out of order, the first required motor torque is set to 0,and the zero torque control of the first drive motor Mr is executed (seeFIG. 9B).

In a case where the value of the regeneration flag is “1,” the drivingforce distribution calculation unit 721 calculates the first torqueratio Rr and the second torque ratio Rf so that the ratio between thetorque of the first drive motor Mr and the torque of the second drivemotor Mf is configured such that, for example, the torque of the firstdrive motor Mr becomes smaller than the torque of the second drive motorMf, more specifically, is set to, for example 30:70. That is, in thiscase, the first torque ratio Rr is set to 0.30, and the second torqueratio Rf is set to 0.70. In the driving force distribution calculationunit 721, the second torque ratio Rf is made larger than the firsttorque ratio Rr in this manner, and thus the second regenerativeelectric power that is supplied from the second inverter 3 f to thesecond power line 22 during regenerative deceleration can be made largerthan the first regenerative electric power that is supplied from thefirst inverter 3 r to the first power line 21.

Next, in S202, the driving force distribution calculation unit 721calculates the first required power and the second required power bymultiplying vehicle required power calculated by the required powercalculation unit 70 by the first torque ratio Rr or the second torqueratio Rf. That is, the required power calculation unit 70 sets a valueobtained by multiplying the vehicle required power by the first torqueratio Rr as the first required power, and sets a value obtained bymultiplying the vehicle required power by the second torque ratio Rf asthe second required power. However, in a case where the zero torquecontrol is executed as described above, power required for performingthe zero torque control is added to required power for a target drivemotor.

Next, in S203, the driving force distribution calculation unit 721performs a motor limit process on the first required power and thesecond required power calculated in S202. This motor limit process is aprocess of limiting the vehicle required power in accordance with thestates of the drive motors Mr and Mf. More specifically, the drivingforce distribution calculation unit 721 calculates a first torque limitand a second torque limit that are upper limits of torques capable ofbeing output by the respective drive motors Mr and Mf in accordance witha known algorithm, and calculates a first output limit and a secondoutput limit by converting these torque limits into electric power. Asshown in the following Expression (1), the driving force distributioncalculation unit 721 sets the smaller of the first required power andthe first output limit as first required power after motor limit. Asshown in the following Expression (2), the driving force distributioncalculation unit 721 sets the smaller of the second required power andthe second output limit as second required power after motor limit.Meanwhile, hereinafter, the first required power after motor limit isdenoted by “first required power′,” and the second required power aftermotor limit is denoted by “second required power′.”First required power′=MIN[first required power,first output limit]  (1)Second required power′=MIN[second required power,second outputlimit]  (2)

Next, in S204, the driving force distribution calculation unit 721 usesfirst required power′ and the second required power′ calculated in S203to calculate a first torque ratio Rr′ after limit and a second torqueratio Rf after limit. More specifically, the driving force distributioncalculation unit 721 sets a value obtained by dividing the firstrequired power′ by the sum of the first required power′ and the secondrequired power′ as the first torque ratio Rr′ after limit, and sets avalue obtained by dividing the second required power′ by the above sumas the second torque ratio Rf after limit.

Next, in S205, the driving force distribution calculation unit 721performs a battery limit process on the first required power′ and thesecond required power′ calculated in S203. This battery limit process isa process of limiting the vehicle required power in accordance with thestates of the first battery B1 and the second battery B2. Morespecifically, the driving force distribution calculation unit 721acquires battery composition limit power (that is, a combination ofoutputtable power and regenerable electric power) calculated by thecomposition limit power calculation unit 731. In addition, as shown inthe following Expression (3), the driving force distribution calculationunit 721 sets the smaller of a value obtained by multiplying the batterycomposition limit power by the first torque ratio Rr′ after limit andthe first required power′ as first required power after battery limit.In addition, as shown in the following Expression (4), the driving forcedistribution calculation unit 721 sets the smaller of a value obtainedby multiplying the battery composition limit power by the second torqueratio Rf after limit and the second required power′ as second requiredpower after battery limit. Meanwhile, in arithmetic operations of thefollowing Expression (3) and (4), the driving force distributioncalculation unit 721 uses positive outputtable power as the batterycomposition limit power in a case where the first required power aftermotor limit and the second required power after motor limit arepositive, and uses negative regenerable electric power as the batterycomposition limit power in a case where the first required power aftermotor limit and the second required power after motor limit arenegative. In addition, hereinafter, the first required power afterbattery limit is denoted by “first required power″,” and the secondrequired power after battery limit is denoted by “second requiredpower″.”First required power″=MIN[battery composition limit power×Rr′,firstrequired power′]  (3)Second required power″=MIN[battery composition limit power×Rf′,secondrequired power′]  (4)

Next, in S206, the driving force distribution calculation unit 721converts the units of the first required power″ and the second requiredpower″ calculated in S205 by using the number of motor rotations, tothereby calculate the first required motor torque and the secondrequired motor torque.

Next, a specific arithmetic procedure of the energy distributioncalculation unit 732 will be described with reference to FIG. 25.

FIG. 25 is a functional block diagram illustrating a procedure ofcalculating required passage power in the energy distributioncalculation unit 732.

The energy distribution calculation unit 732 includes a basic passagepower calculation unit 7321 that calculates basic passage power, aregenerative traveling state passage power calculation unit 7322 thatcalculates regeneration state passage power, a high-output travelingstate passage power calculation unit 7323 that calculate high-outputtraveling state passage power, an electrical pass state passage powercalculation unit 7324 that calculates electrical pass state passagepower, an idle state passage power calculation unit 7325 that calculatesidle state passage power, and a required passage power calculation unit7326 that calculates required passage power by adding up the basicpassage power, the regeneration state passage power, the high-outputtraveling state passage power, and the idle state passage power.

The basic passage power calculation unit 7321 calculates the basicpassage power equivalent to a basic value for the required passagepower. In a case where the value of the driving state flag is any of“0,” “2” and “5,” the basic passage power calculation unit 7321calculates the basic passage power in accordance with the followingprocedure. In addition, in case where the value of the driving stateflag is neither of “0,” “2” and “5,” the basic passage power calculationunit 7321 sets the basic passage power to 0.

In a case where the value of the driving state flag is “0” or “5” andthe value of the second battery usage flag is “1” or the value of thesecond battery failure flag is “1,” the basic passage power calculationunit 7321 sets a value obtained by adding up the second required power″calculated in the driving force distribution calculation unit 721 andrequired power in the vehicle accessory H as the basic passage power.Thereby, for example, a flow of power shown in FIG. 4A or 9A isrealized.

-   -   [Driving state flag=0, second use battery flag=1]    -   [Driving state flag=5, second battery failure flag=1]        Basic passage power=second required power″+accessory required        power

In a case where the value of the driving state flag is “0,” the value ofthe second battery usage flag is “0,” and the value of the second SOCconsumption flag is “1,” that is, in a case where the driving state is anormal traveling state and the consumption of the second SOC of thesecond battery B2 is required, the basic passage power calculation unit7321 calculates the basic passage power in accordance with the followingprocedure so that the flow of power shown in FIG. 4C is realized. Inthis case, the basic passage power calculation unit 7321 calculates atarget power ratio r that is a ratio of power discharged from the secondbattery B2 to power discharged from the first battery B1 and the secondbattery B2 on the basis of the second SOC of the second battery B2. Thebasic passage power calculation unit 7321 calculates the target powerratio r by searching a map as shown in FIG. 26 on the basis of thesecond SOC. According to an example of the map shown in FIG. 26, as thesecond SOC becomes larger, the target power ratio r also becomes higher.That is, as the second SOC becomes larger, the burden of the secondbattery B2 becomes larger. The basic passage power calculation unit 7321uses the target power ratio r calculated in this manner to calculate thebasic passage power using the following expression. Thereby, the flow ofpower shown in FIG. 4C is realized.

-   -   [Driving state flag=0, second battery usage flag=0, second SOC        consumption flag=1]        Basic passage power=(1−r)×(second required power″+accessory        required power)−r first required power″

In a case where the value of the driving state flag is “2” and the valueof the voltage converter deactivation request flag is “0,” the basicpassage power calculation unit 7321 sets a value obtained by combiningthe second required power″ required for performing the zero torquecontrol on the second drive motor Mf with the required power of thevehicle accessory H as the basic passage power so that the flow of powershown in FIG. 6B is realized. Thereby, in a case where the value of theelectrical pass execution flag is “1,” and electrical pass state passagepower to be described later is applied, the flow of power shown in FIG.6B is realized.

-   -   [Driving state flag=2, voltage converter deactivation request        flag=0]        Basic passage power=second required power″+accessory required        power

In a case where the value of the driving state flag is “5” and the valueof the first battery failure flag is “1,” the basic passage powercalculation unit 7321 sets a value obtained by multiplying the firstrequired power″ required for performing the zero torque control on thefirst drive motor Mr by “−1” as the basic passage power so that the flowof power shown in FIG. 9B is realized. Thereby, the flow of power shownin FIG. 9B is realized.

-   -   [Driving state flag=5, first battery failure flag=1]        Basic passage power=−first required power″

In a case where the value of the driving state flag is “3,” theregenerative traveling state passage power calculation unit 7322calculates the regenerative traveling state passage power in accordancewith the following procedure. In a case where the value of the drivingstate flag is not “3,” the regenerative traveling state passage powercalculation unit 7322 sets the regenerative traveling state passagepower to 0. Meanwhile, in a case where the value of the driving stateflag is “3,” both the first required power″ and the second requiredpower″ are set to be negative.

In a case where both the values of the first battery usage flag and thesecond battery usage flag are “0” and the second SOC is within thesecond basic regeneration permission range, the regenerative travelingstate passage power calculation unit 7322 sets a value, obtained bysubtracting the second regenerable electric power that is negative fromthe sum of the second required power″ that is negative and the accessoryrequired power that is positive, as the regenerative traveling statepassage power so that the second battery B2 is preferentially charged.This is equivalent to the supply of an amount, that is not able to beconsumed in driving of the vehicle accessory H and charging of thesecond battery B2 in regenerative electric power supplied from thesecond drive motor Mf to the second power line 22, to the first batteryB1. Thereby, it is possible to preferentially charge the second batteryB2 rather than the first battery B1 while realizing the flow of powershown in FIG. 7A.

-   -   [Driving state flag=3, first and second battery usage flags=0,        the second SOC is within the second basic regeneration        permission range]        Regenerative traveling state passage power=second required        power″+accessory required power−second regenerable electric        power

In a case where both the values of the first battery usage flag and thesecond battery usage flag are “0” and the second SOC is out of thesecond basic regeneration permission range, the regenerative travelingstate passage power calculation unit 7322 sets a value, obtained bysubtracting the first required power″ that is negative from the firstregenerable electric power that is negative, as the regenerativetraveling state passage power so that the first battery B1 ispreferentially charged. This is equivalent to the supply of thisshortage from the second power line 22 to the first battery B1 in a casewhere there is remaining power even when all regenerative electric powersupplied from the first drive motor Mr to the first power line 21 issupplied to the first battery B1. Thereby, it is possible topreferentially charge the first battery B1 rather than the secondbattery B2 while realizing the flow of power shown in FIG. 7A.

-   -   [Driving state flag=3, first and second battery usage flags=0,        the second SOC is out of the second basic regeneration        permission range]        Regenerative traveling state passage power=first regenerable        electric power−first required power″

In a case where the value of the first battery usage flag is “0” and thevalue of the second battery usage flag is “2,” the regenerativetraveling state passage power calculation unit 7322 sets the sum of thesecond required power″ that is negative and the accessory required powerthat is positive as the regenerative traveling state passage power. Thisis equivalent to the supply of an amount, that is not able to beconsumed in driving of the vehicle accessory H in regenerative electricpower supplied from the second drive motor Mf to the second power line22, to the first battery B1. Thereby, it is possible to realize the flowof power shown in FIG. 7B.

-   -   [Driving state flag=3, first battery usage flag=0, second        battery usage flag=2]        Regenerative traveling state passage power=second required        power″+accessory required power

In a case where the value of the first battery usage flag is “2” and thevalue of the second battery usage flag is “0,” the regenerativetraveling state passage power calculation unit 7322 sets a valueobtained by multiplying the first required power″ that is negative by“−1” as the regenerative traveling state passage power. This isequivalent to the supply of all regenerative electric power suppliedfrom the first drive motor Mr to the first power line 21 to the secondpower line 22, and the use of the supplied electric power in driving ofthe vehicle accessory H and charging of the second battery B2. Thereby,it is possible to realize the flow of power shown in FIG. 7C.

-   -   [Driving state flag=3, first battery usage flag=2, second        battery usage flag=0]        Regenerative traveling state passage power=−first required        power″

In a case where both the values of the first battery usage flag and thesecond battery usage flag are “2,” the regenerative traveling statepassage power calculation unit 7322 sets the regenerative travelingstate passage power to 0. Thereby, it is possible to realize the flow ofpower shown in FIG. 7D.

-   -   [Driving state flag=3, first battery usage flag=2, second        battery usage flag=2]        Regenerative traveling state passage power=0

In a case where the value of the driving state flag is “1” and the valueof the second battery usage flag is “0,” the high-output traveling statepassage power calculation unit 7323 calculates the high-output travelingstate passage power in accordance with the following procedure. Inaddition, in a case where the value of the driving state flag is not“1,” the high-output traveling state passage power calculation unit 7323sets the high-output traveling state passage power to 0. As describedabove, in a case where the total required power exceeds the firstoutputtable power that is an upper limit of power capable of beingoutput by the first battery B1, the driving state is set as ahigh-output traveling state. In this high-output traveling state, thesecond battery B2 is discharged so as to compensate for a shortagecaused by the first battery B1. Consequently, the high-output travelingstate passage power calculation unit 7323 sets a value obtained bysubtracting the first required power″ from the first outputtable poweras the high-output traveling state passage power. Thereby, the flow ofpower shown in FIG. 5 is realized.

-   -   [Driving state flag=1, second battery usage flag=0]        High−output traveling state passage power=first outputtable        power−first required power″

Only in a case where the value of the electrical pass execution flag is“1,” the electrical pass state passage power calculation unit 7324calculates the positive electrical pass state passage power inaccordance with the following procedure. In addition, in a case wherethe value of the electrical pass execution flag is not “1,” theelectrical pass state passage power calculation unit 7324 sets theelectrical pass state passage power to 0. Thereby, in a case where thevalue of the electrical pass execution flag is set to “1,” for example,when the driving state is a normal traveling state, the flow of powershown in FIG. 4B is realized, and the electrical pass state passagepower is supplied to the second battery B2. In addition, in a case wherethe value of the electrical pass execution flag is set to “1” when thedriving state is a low-output traveling state, the flow of power shownin FIG. 6B is realized, and the electrical pass state passage power issupplied to the second battery B2. In addition, in a case where thevalue of the electrical pass execution flag is set to “1” when thedriving state is a regenerative traveling state, the flow of power shownin FIG. 7E is realized, and the electrical pass state passage power issupplied to the second battery B2.

The magnitude of this electrical pass state passage power may be a fixedvalue determined in advance, or may be a variable value. In addition, inthe case of a variable value, the magnitude of the electrical pass statepassage power may be changed, for example, in accordance with thepresence or absence of the execution of a recovery mode. That is, in acase where the recovery mode is being executed, the electrical passstate passage power may be made larger than in a case where the recoverymode is not being executed. Thereby, in a case where the recovery modeis being executed, power with which the second power storage device ischarged by executing the electrical pass control can be made larger thanin a case where the recovery mode is not being executed, whereby it ispossible to quickly recover the second SOC. In addition, in the case ofa variable value, the magnitude of the electrical pass state passagepower may be changed, for example, in accordance with the second SOC.

In a case where the value of the driving state flag is “4,” the idlestate passage power calculation unit 7325 calculates the idle statepassage power in accordance with the following procedure. In addition,in a case where the value of the driving state flag is not “4,” the idlestate passage power calculation unit 7325 sets the idle state passagepower to 0.

In a case where the value of the driving state flag is “4” and the valueof the second battery usage flag is “0,” the idle state passage powercalculation unit 7325 sets the idle state passage power to 0. Thereby,the flow of power shown in FIG. 8A is realized.

-   -   [Driving state flag=4, second battery usage flag=0]        Idle state passage power=0

In a case where the value of the driving state flag is “4” and the valueof the second battery usage flag is “1,” the idle state passage powercalculation unit 7325 sets the required power in the vehicle accessory Has the idle state passage power. Thereby, the flow of power shown inFIG. 8B is realized.

-   -   [Driving state flag=4, second battery usage flag=1]        Idle state passage power=accessory required power

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed embodimentswithout departing from the scope or spirit of the disclosure. In view ofthe foregoing, it is intended that the disclosure covers modificationsand variations provided that they fall within the scope of the followingclaims and their equivalents.

What is claimed is:
 1. A vehicle power supply system comprising: a firstmotor generator connected to a first wheel of a vehicle; a second motorgenerator connected to a second wheel; a first power line to which afirst power converter that transfers power to and from the first motorgenerator and a first power storage device are connected; a second powerline to which a second power converter that transfers power to and fromthe second motor generator and a second power storage device areconnected; a voltage converter that converts a voltage between the firstpower line and the second power line; and a charging and dischargingcontrol device that controls charging and discharging of the first andsecond power storage devices by operating the first and second powerconverters and the voltage converter, wherein the charging anddischarging control device further comprises a limit power calculationunit that acquires a regenerable electric power that is an upper limitpower for regenerative electric power supplied to the second powerstorage device during regenerative deceleration in which theregenerative electric power is generated by the first and second motorgenerators, and the charging and discharging control device charges thesecond power storage device with the regenerative electric power duringthe regenerative deceleration, and supplies a surplus regenerativeelectric power of the regenerative electric power to the voltageconverter when the regenerative electric power is larger than theregenerable electric power, wherein the surplus regenerative electricpower is obtained by excluding the regenerable electric power from theregenerative electric power.
 2. The vehicle power supply systemaccording to claim 1, wherein a vehicle accessory that is an electricalload is connected to the second power line, and the charging anddischarging control device charges the second power storage device anddrives the vehicle accessory with the regenerative electric power, andsets the surplus regenerative electric power by excluding theregenerable electric power and power required in the vehicle accessoryfrom the regenerative electric power.
 3. The vehicle power supply systemaccording to claim 1, wherein the first power storage device is lower inoutput weight density and is higher in energy weight density than thesecond power storage device.
 4. The vehicle power supply systemaccording to claim 1, wherein the first wheel is a rear wheel and thesecond wheel is a front wheel, and during the regenerative deceleration,the charging and discharging control device operates the first andsecond power converters so that the regenerative electric power becomeslarger than a further regenerative electric power that is power suppliedfrom the first power converter to the first power line during theregenerative deceleration.
 5. The vehicle power supply system accordingto claim 1, further comprising: a second power storage parameteracquisition unit that acquires a value of a second power storageparameter increasing in accordance with an amount of power storage ofthe second power storage device; and a second regeneration permissionupper limit setting unit that sets a second regeneration permissionupper limit that is a threshold for the second power storage parameter,wherein, when the value of the second power storage parameter is largerthan the second regeneration permission upper limit during theregenerative deceleration, the charging and discharging control deviceprohibits the second power storage device from being charged, andsupplies at least a portion of the regenerative electric power to thefirst power storage device through the voltage converter and the firstpower line.
 6. The vehicle power supply system according to claim 1,further comprising: a second power storage parameter acquisition unitthat acquires a value of a second power storage parameter increasing inaccordance with an amount of power storage of the second power storagedevice; and a second regeneration permission upper limit setting unitthat sets a second regeneration permission upper limit that is athreshold for the second power storage parameter, wherein the chargingand discharging control device prohibits the second power storage devicefrom being charged when the value of the second power storage parameteris larger than the second regeneration permission upper limit during theregenerative deceleration, and the second regeneration permission upperlimit setting unit changes the second regeneration permission upperlimit on the basis of a state of the first power storage device.
 7. Thevehicle power supply system according to claim 5, wherein the secondregeneration permission upper limit setting unit changes the secondregeneration permission upper limit on the basis of a state of the firstpower storage device.
 8. The vehicle power supply system according toclaim 7, further comprising: a first power storage parameter acquisitionunit that acquires a value of a first power storage parameter increasingin accordance with an amount of power storage of the first power storagedevice; and a first regeneration permission upper limit setting unitthat sets a first regeneration permission upper limit that is athreshold for the first power storage parameter, wherein, when the valueof the first power storage parameter is larger than the firstregeneration permission upper limit, the second regeneration permissionupper limit setting unit makes the second regeneration permission upperlimit larger than when the value of the first power storage parameter isequal to or less than the first regeneration permission upper limit, andthe charging and discharging control device prohibits the first powerstorage device from being charged when the value of the first powerstorage parameter is larger than the first regeneration permission upperlimit during the regenerative deceleration.
 9. The vehicle power supplysystem according to claim 6, wherein the second regeneration permissionupper limit setting unit sets the second regeneration permission upperlimit as a value of any of a predetermined first threshold and a secondthreshold larger than the first threshold, and the second regenerationpermission upper limit setting unit sets the second regenerationpermission upper limit as the first threshold when the value of thesecond power storage parameter is equal to or less than the firstthreshold during the regenerative deceleration, and sets the secondregeneration permission upper limit as a value of any of the firstthreshold and the second threshold on the basis of the state of thefirst power storage device when the value of the second power storageparameter is larger than the first threshold and equal to or less thanthe second threshold.
 10. The vehicle power supply system according toclaim 9, wherein the limit power calculation unit acquires anotherregenerable electric power that is an upper limit power for regenerativeelectric power supplied to the first power storage device during theregenerative deceleration, wherein the second regeneration permissionupper limit setting unit sets the second regeneration permission upperlimit as the second threshold when the value of the second power storageparameter is larger than the first threshold and equal to or less thanthe second threshold during the regenerative deceleration, and requiredregenerative electric power is larger than the further regenerableelectric power.
 11. The vehicle power supply system according to claim2, wherein the first power storage device is lower in output weightdensity and is higher in energy weight density than the second powerstorage device.
 12. The vehicle power supply system according to claim2, wherein the first wheel is a rear wheel and the second wheel is afront wheel, and during the regenerative deceleration, the charging anddischarging control device operates the first and second powerconverters so that the regenerative electric power becomes larger than afurther regenerative electric power that is power supplied from thefirst power converter to the first power line during the regenerativedeceleration.
 13. The vehicle power supply system according to claim 3,wherein the first wheel is a rear wheel and the second wheel is a frontwheel, and during the regenerative deceleration, the charging anddischarging control device operates the first and second powerconverters so that the regenerative electric power becomes larger than afurther regenerative electric power that is power supplied from thefirst power converter to the first power line during the regenerativedeceleration.
 14. The vehicle power supply system according to claim 2,further comprising: a second power storage parameter acquisition unitthat acquires a value of a second power storage parameter increasing inaccordance with an amount of power storage of the second power storagedevice; and a second regeneration permission upper limit setting unitthat sets a second regeneration permission upper limit that is athreshold for the second power storage parameter, wherein, when thevalue of the second power storage parameter is larger than the secondregeneration permission upper limit during the regenerativedeceleration, the charging and discharging control device prohibits thesecond power storage device from being charged, and supplies at least aportion of the regenerative electric power to the first power storagedevice through the voltage converter and the first power line.
 15. Thevehicle power supply system according to claim 3, further comprising: asecond power storage parameter acquisition unit that acquires a value ofa second power storage parameter increasing in accordance with an amountof power storage of the second power storage device; and a secondregeneration permission upper limit setting unit that sets a secondregeneration permission upper limit that is a threshold for the secondpower storage parameter, wherein, when the value of the second powerstorage parameter is larger than the second regeneration permissionupper limit during the regenerative deceleration, the charging anddischarging control device prohibits the second power storage devicefrom being charged, and supplies at least a portion of the regenerativeelectric power to the first power storage device through the voltageconverter and the first power line.
 16. The vehicle power supply systemaccording to claim 4, further comprising: a second power storageparameter acquisition unit that acquires a value of a second powerstorage parameter increasing in accordance with an amount of powerstorage of the second power storage device; and a second regenerationpermission upper limit setting unit that sets a second regenerationpermission upper limit that is a threshold for the second power storageparameter, wherein, when the value of the second power storage parameteris larger than the second regeneration permission upper limit during theregenerative deceleration, the charging and discharging control deviceprohibits the second power storage device from being charged, andsupplies at least a portion of the regenerative electric power to thefirst power storage device through the voltage converter and the firstpower line.
 17. The vehicle power supply system according to claim 2,further comprising: a second power storage parameter acquisition unitthat acquires a value of a second power storage parameter increasing inaccordance with an amount of power storage of the second power storagedevice; and a second regeneration permission upper limit setting unitthat sets a second regeneration permission upper limit that is athreshold for the second power storage parameter, wherein the chargingand discharging control device prohibits the second power storage devicefrom being charged when the value of the second power storage parameteris larger than the second regeneration permission upper limit during theregenerative deceleration, and the second regeneration permission upperlimit setting unit changes the second regeneration permission upperlimit on the basis of a state of the first power storage device.
 18. Thevehicle power supply system according to claim 3, further comprising: asecond power storage parameter acquisition unit that acquires a value ofa second power storage parameter increasing in accordance with an amountof power storage of the second power storage device; and a secondregeneration permission upper limit setting unit that sets a secondregeneration permission upper limit that is a threshold for the secondpower storage parameter, wherein the charging and discharging controldevice prohibits the second power storage device from being charged whenthe value of the second power storage parameter is larger than thesecond regeneration permission upper limit during the regenerativedeceleration, and the second regeneration permission upper limit settingunit changes the second regeneration permission upper limit on the basisof a state of the first power storage device.
 19. The vehicle powersupply system according to claim 4, further comprising: a second powerstorage parameter acquisition unit that acquires a value of a secondpower storage parameter increasing in accordance with an amount of powerstorage of the second power storage device; and a second regenerationpermission upper limit setting unit that sets a second regenerationpermission upper limit that is a threshold for the second power storageparameter, wherein the charging and discharging control device prohibitsthe second power storage device from being charged when the value of thesecond power storage parameter is larger than the second regenerationpermission upper limit during the regenerative deceleration, and thesecond regeneration permission upper limit setting unit changes thesecond regeneration permission upper limit on the basis of a state ofthe first power storage device.
 20. The vehicle power supply systemaccording to claim 7, wherein the second regeneration permission upperlimit setting unit sets the second regeneration permission upper limitas a value of any of a predetermined first threshold and a secondthreshold larger than the first threshold, and the second regenerationpermission upper limit setting unit sets the second regenerationpermission upper limit as the first threshold when the value of thesecond power storage parameter is equal to or less than the firstthreshold during the regenerative deceleration, and sets the secondregeneration permission upper limit as a value of any of the firstthreshold and the second threshold on the basis of the state of thefirst power storage device when the value of the second power storageparameter is larger than the first threshold and equal to or less thanthe second threshold.